Experienced and professional animal trainer provide their insights in answering this question :
A. You should see a specialist and find out what is causing the aggression. Some more info are necessary to make a diagnosis. It can be connected with territorial competition, sexual excitement, boredom and others.

How to Identify Common Pet Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced pet care professionals :

A long-lasting fear of other dogs can result, and this fear can trigger an aggressive response. Because genetic and early environmental factors contribute to behavior, even well-socialized dogs can develop aggression toward other dogs.
If your dog is aggressive towards all dogs, start by exposing them to small doses of positive experiences with other dogs. This could be in the form of doggy playdates, or even just walking past other dogs on the street. The key is to go slowly and let your dog set the pace.
However, there`s no guarantee that an aggressive dog can be completely cured. In many cases, the only solution is to manage the problem by limiting a dog`s exposure to the situations, people or things that trigger her aggression. There`s always risk when dealing with an aggressive dog.
For dogs exhibiting territorial aggression, you will need to gain enough control to have your dog sit, stay, and when calmed down, take a reward at the front door. Generally, a leash and head collar will give the fastest and most effective control (see Training Products – Head Halter Training).
There is no real cure for inter-dog aggression. Instead, treatment is heavily focused on controlling the problem. Owners must learn how to avoid situations that encourage aggressive behavior in the dog, and to break up fights quickly and safely when they occur.
If the dog is afraid of other dogs, letting him look away and then move away from the other dog is the best reinforcement for most dogs. You can start this by teaching an Autowatch, or by waiting for him to look away himself, and reinforce it with food, play and/or an increase in distance between the dogs.
Any breed can be reactive, but it`s especially common in the herding types, like border collies and cattle dogs. These dogs were bred for laser focus and the ability to instantly react to changes in their environment.
If your dog is showing any changes in their behaviour, especially if they have started showing aggression suddenly, you should contact your vet as soon as possible. Aggression tends to get worse over time and can lead to serious injuries to you, your dog or other people and pets so getting help is essential.
Introduce on neutral territory.

Each dog should be walked separately on a leash, and each walker should have a bag of high-value treats or food broken into small pieces. At first, walk the dogs at a distance where they can see each other but are not too provoked by each other`s presence.

If left unchecked, serious fighting can ensue resulting in injury or even death. Fighting occurs because the dogs have not established a stable dominance hierarchy. Dogs have no sense of equality, so one must always be the leader. This is often a difficult concept for owners to grasp.
For a Jack Russell that is very aggressive with other dogs, a technique is to squirt the terrier in the face with water whenever he growled at other dogs. No scolding or other action is required in this instance – just a surprise squirt. A Jack Russell Terrier that bites can be a big problem.
Move your dog closer to the other dog one foot at a time. Keep your dog below threshold, only decreasing the distance when your dog is anticipating the treat. Once your dog can be next to the still, quiet dog, return to the 20-foot distance and have the other dog move parallel to your dog.
Avoid approaching other dogs head-on.

If you find yourself approaching another dog head-on, simply go around them in an arc, keeping your dog`s attention as suggested above. If the other dog starts to lunge and bark, keep your pup`s attention and reward more often. As soon as the other dog is gone, so are the treats.

Are you surprised by the findings? Rough Collies are the most aggressive dog breed, a new study of more than 9,000 pets has found. Research conducted by the University of Helsinki found that smaller dogs are more likely to behave aggressively, growl, snap, and bark compared to mid-sized and large dogs.
Genetics, lack of socialization, insufficient training to learn self-control, a frightening experience, or a combination of these can cause reactivity, and fear is typically the driving force.
Dog to dog aggression is likely to increase during sexual maturity as dogs become more concerned with establishing territory, social status and access to potential mates. Adulthood. This is the period when adolescence ends – usually sometime between 1-3 years of age depending upon the breed and individual dog.
If your dog suddenly becomes more aggressive, schedule an exam with their regular veterinarian to check for underlying conditions that may be causing the sudden aggression. Your vet will likely do a physical and, if necessary, a neurological exam.
There are multiple reasons that a dog may exhibit aggression toward family members. The most common causes include conflict aggression, fear-based, defensive aggression, status related aggression, possessive aggression, food guarding aggression and redirected aggression.
Can dogs live together after fighting? The answer is, most of the time, YES. There are times when dogs may be like an incompatible couple and need to divorce, but in general, there are things you can do to help combative pups get along.
In dogdom, there`s a turn of phrase called, “Second Dog Syndrome”. This describes the process of adding another dog to the home quite well, but not necessarily in a positive light. As humans, we are bound to forget all of the time and effort it takes to raise a puppy right.
Many people do not give two dogs time to adequately adjust to one another before deciding that having two dogs will simply not work. It can take up to one month for an old dog and new dog to really settle in and accept each other`s position in the pack.
This may make it hard to tell the difference between playing and fighting. The key is to make sure both dogs are engaging at similar levels and do not look stressed. If both dogs are play bowing, bouncy, or seem to exaggerate their movements and vocalizations, it`s likely a play session.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

Q. How do I determine how much my overweight pet should weigh?
ANSWER : A. There are many tools to determine overweight and obesity levels in pets. A new tool, morphometric measurements and body fat index, are available to accurately determine a pet’s ideal weight; this will allow an accurate determination of the amount of food a pet should receive to achieve weight loss. Feeding the correct amount will lead to greater weight loss success.

There are many weight loss food options to help pets reach their ideal weight. Your veterinarian can help make a ideal weight recommendation. Here are some tips to help your dog lose weight in a healthy and safe way:

1. Diet: Providing a healthy and well balanced diet is essential to your pet’s overall health. Finding the right food for your dog can be a challenging process. For those overweight animals many commercial dog companies offer weight loss diets, but it is important to evaluate food labels for adequate nutritional content.

You want to ensure you are not missing other essential vitamin or mineral content. Volume of food is also important and the amount of food that works for one breed of dog may not be the same for another breed of dog. Portion control as opposed to free-choice feeding can help your dog to drop a few unnecessary pounds.

There are also prescription weight loss foods designed by veterinary nutritionists, such as Hill’s r/d (http://bit.ly/1AoENSd). Some pet owners find that home cooking is the best option for helping to provide a well-balanced and realistic diet plan. There are websites such as balanceit.com that offers recipes to fit your dog’s specific needs. Consulting with your veterinarian or a veterinary nutritionist to find the appropriate diet is a great way to help your dog be as healthy as possible.

2. Exercise: Another great tactic for weight loss for your dog is exercise. Whether this is through running, walking or playing with a favorite toy all of these are wonderful types of exercise to help keep your dog at a lean and healthy weight.

For those pet owners with busy schedules utilizing professional dog walking services or playtime through dog daycare services is another option. It has been shown that those pet owners that exercise regularly with their pets generally live a healthier lifestyle.

3. Physical therapy: As animals age pet owners offer encounter their favorite canine having more difficulty walking and have a dwindling desire to play with toys. Physical therapy, specifically hydrotherapy is a wonderful way to help older and arthritic animals gain more mobility and lose weight. Hydrotherapy has been proven to have several therapeutic effects on the body including, muscle strengthening, relief of swelling, decreased joint pain, less stiffness in limbs, improved circulation, weight loss, and increased tissue healing to name a few. For more information on the benefits of hydrotherapy:
http://bit.ly/1w1qqoy

4. Veterinary visit and blood work: Weight gain can also be related to underlying health concerns such as hypothyroidism or other endocrine disorders. Scheduling a veterinary evaluation and routine blood work can be another important component in increasing the longevity of your dog’s life. Conditions such as hypothyroidism that predispose dogs to gain weight can be treated with a daily medication to improve hormonal balance. If feel that your dog is unnecessarily overweight there can be an underlying health condition that needs to be addressed.

5. Healthy treats: Pet owners love the chance to reward their favorite canine companion with treats and most dogs jump at the chance to consume these delicious products. The problem is many treats, which can include commercial dog treats or table scrapes can add many unnecessary calories to your dog’s daily intake. Reading labels and making note of the calories in these treats is an important component of understanding your dog’s overall health. Treats should not exceed more than 10 percent of your pet’s daily calories. There are healthier treats that can be offered to your pet to keep calories lower yet provide a fuller sensation. A pet owner can add steamed or pureed vegetables, such as carrots, green beans or sweet potato to add more fiber and thus a fuller feeling for your dog.

Q. Whenever I take my dog on walks he always barks at people and others dogs in my neighborhood. What should I do to resolve the problem
ANSWER : A. The very first thing to do is to make sure your dog is getting sufficient physical and mental exercise every day. A tired dog is a good, happy dog and one who is less likely to bark from boredom or frustration. Depending on his breed, age, and health, your dog may require several long walks as well as a good game of chasing the ball and playing with some interactive toys.

Figure out what he gets out of barking and remove it. Don’t give your dog the opportunity to continue the barking behavior.

Ignore your dog’s barking for as long as it takes him to stop. That means don’t give him attention at all while he’s barking. Your attention only rewards him for being noisy. Don’t talk to, don’t touch, or even look at him. When he finally quiets, even to take a breath, reward him with a treat. To be successful with this method, you must wait as long as it takes for him to stop barking. Yelling at him is the equivalent of barking with him.

Get your dog accustomed to whatever causes him to bark. Start with whatever makes him bark at a distance. It must be far enough away that he doesn’t bark when he sees it. Feed him lots of good treats. Move the stimulus a little closer (perhaps as little as a few inches or a few feet to start) and feed treats. If the stimulus moves out of sight, stop giving your dog treats. You want your dog to learn that the appearance of the stimulus leads to good things.

Teach your dog the ‘quiet’ command. Oddly, the first step is to teach your dog to bark on command. Give your dog the command to “speak,” wait for him to bark two or three times, and then stick a tasty treat in front of his nose. When he stops barking to sniff the treat, praise him and give him the treat. Repeat until he starts barking as soon as you say “speak.” Once your dog can reliably bark on command, teach him the “quiet” command. In a calm environment with no distractions, tell him to “speak.” When he starts barking, say “quiet” and stick a treat in front of his nose. Praise him for being quiet and give him the treat.

As in all training, always end training on a good note, even if it is just for obeying something very simple, like the ‘sit’ command. If you dog regresses in training, go back to the last thing he did successfully and reinforce that before moving on again. Keep sessions short, 15-20 minutes max, and do this several times a day.

Q. Rescued a dog almost two weeks ago, and now that her kennel cough is gone her personality shines!! No previous training, how should I start?
ANSWER : A. POST FOUR:

After your dog is familiar with the behavior you lured from scratch, and taught to your dog, you can start to use the “no-reward marker” I talked about. What you do is ask the dog to perform the behavior, and if the dog does not perform the behavior, you simply say your no-reward marker (choose one: eh-eh, hey, uh-oh, oops) show them the treat, put it behind your back, and BRIEFLY ignore your dog. Just turn your back for a second or two, before turning back to your dog and saying, “let’s try that again.” When you’re ready to start over with your dog, make sure you move around. If you are repeating the same cue while in the same position, while your dog is in the same position, you are likely to receive the same results. The more you move around, and start fresh, the better your chances are of having your dog listen to your cue the second time around. BIG rewards when they dog it successfully! Lots of praise and treats.

My no-reward marker is “hey.” When my dog does something wrong I say, “hey” and she immediately understands that she needs to offer a different behavior. This is clear to her. I don’t have to say it in a mean way, I simply say, “hey” in a normal tone of voice and she understands what the word means.

Once you’ve built up that connection and communication with your new dog, you can work on all kinds of fun behaviors! I personally enjoy the more zen-like behaviors: https://www.youtube.com/watch?v=ruy9UMcuGh8

I like to teach my dog fun tricks that offer her a “job” to do of sorts like object retrieval: https://www.youtube.com/watch?v=I4iertZSva8

(object retrieval training completed; what it looks like: https://www.youtube.com/watch?v=jx0Dml28FGY)

Scent-games are fun too! Very confidence building. Hide a REALLY smelly treat in a box, and place that box in a line of boxes. Let your dog go in the room while saying something like “search!” or “find it!” and watch them hunt for that smelly treat! Lots of rewards when they find it!

Q. My Bulldog puppy growls, barks and even tries to bite me when I say “no” to him. What can I do?
ANSWER : A. First, avoid scolding him and acting aggressively towards him if you don’t want him to be acting aggressively towards you. There are other methods you can use to communicate to your dog that you don’t want him to continue doing what he is doing. I recommend you stop telling him “no”, scolding him, or raising your voice at him. Everything coming from you should be 100% positive and 100% calm.

Try to figure out ways to clearly communicate what you want to your dog. If you want your dog to leave something or someone alone, I strongly suggest teaching your dog commands like “leave it”. Here is a link to a video in which I explain how to do it:

www.youtube.com/watch?v=R1TS5nA7z5Q

Another thing I suggest you use is a no-reward marker. This clearly communicates when your dog has done something wrong. No-reward markers have to be introduced during your training sessions. You should be doing at least three training sessions per day, that are something like 3-10 minutes long (working on different things each training session). If you are teaching your dog something BRAND NEW, do not use the no-reward marker, as you do not want to discourage your dog from performing behaviors for you. Use the no-reward marker for known behaviors only. Here is another helpful video about this:

www.youtube.com/watch?v=sdU5a6fXKlg

Lure each new behavior (as shown in the video) using high value treats. Let’s say you’re working on “down” which is a behavior your dog knows fairly well. Present the treat to your dog. Ask your dog to “down” (only ask once). If he does not go “down” immediately, say, “uh-oh” or “eh-eh” in a gentle tone, and then place the treat behind your back. This communicates to your dog that they did something to make the treat go away.

After you place the treat behind your back to show your pup “that was wrong” you need to communicate to your pup “let’s try again” by getting your pup to walk around for a second, and then start the behavior all over again. If your puppy is very young, chances are you haven’t taught him a solid “down” behavior yet. So, as I said, do not use this method until you have lured each new behavior as shown in the video.

This is the order in which you should teach behaviors: Lure using a high value treat as shown in the video. After a few successful food lures, lure with an empty hand. If the pup is successful with the empty hand lure, reward with lots of treats. If the pup is unsuccessful, then go back to food-luring a couple more times. After a few successful empty-hand lures, you can begin to add the cue. Say “sit”, then lure with an empty hand, and then reward. Once your pup understands the cue, begin to work on the no-reward marker.

Q. My Beagle listens to me, but cries & whines when I’m gone & doesn’t listen to my parents. I adopted him just a couple days ago. Any tips for my folks?
ANSWER : A. I really highly doubt that your Beagle listens to you and has formed a connection with you in just a couple of days. It takes months to build up any kind of serious connection with your dog. You need to work on communication with your dog through training them to understand different cues. For instance the Leave-It cue: https://www.youtube.com/watch?v=R1TS5nA7z5Q

You have to work on bonding with your dog through mental stimulation. Training is very important. Luring each new behavior from scratch, and training using treats is how you form a strong bond with your new dog. No scolding is ever necessary… work on being calm, and positive, all the time.

If your dog is crying/whining when you leave, this may be separation anxiety. You’re going to have to separation train this dog from scratch. This dog needs to learn that separation can be a good thing! Tell your “folks” to NOT scold the dog when he is crying/whining after you leave, because that will make your dog MORE anxious when you leave next time. Your dog will be dwelling on the negative if your parents fuel your dogs negative feelings towards you leaving. FUN things should happen when you leave. Your parents should pull out the treats and start doing some basic obedience training with your dog. Your parents should stuff a Kong filled with awesome treats (peanut butter) and give it to him so he feels happy when you leave.

I have some excellent separation anxiety exercises you can work on. If you’d like, you can purchase a consultation with me, and I will go over how to separation train from scratch. It will make your dog comfortable being alone, guaranteed.

Read Full Q/A … : I Don't Like My Mother

Q. What can I do to stop my dog from barking at people and front doors?
ANSWER : A. Ignore your dog’s barking for as long as it takes him to stop. This means don’t give him any attention at all while he’s barking. Your attention only rewards him for being noisy. Don’t talk to him, don’t touch him, and don’t even look at him. When he finally quiets down, even to take a breath, reward him with a treat. To be successful with this method, you must wait as long as it takes for him to stop barking. If he barks for an hour and you finally get so frustrated that you yell at him to be quiet, the next time he’ll probably bark for an hour and a half. Dogs learns that if they bark long enough you’ll give them attention.

Teach your dog the ‘quiet’ command. It may sound nonsensical, but the first step is to teach your dog to bark on command. Give your dog the command to “speak,” wait for him to bark two or three times, and then stick a tasty treat in front of his nose. When he stops barking to sniff the treat, praise him and give him the treat. Repeat until he starts barking as soon as you say “speak.” Once your dog can reliably bark on command, teach him the “quiet” command. In a calm environment with no distractions, tell him to “speak.” When he starts barking, say “quiet” and stick a treat in front of his nose. Praise him for being quiet and give him the treat.

When your dog starts barking, ask him to do something that’s incompatible with barking. Teach your dog to react to barking stimuli with something that inhibits him from barking, such as lying down in his bed.

Make sure your dog is getting sufficient physical and mental exercise every day. A tired dog is a good dog and one who is less likely to bark from boredom or frustration. Depending on his breed, age, and health, your dog may require several long walks as well as a good game of fetch and playing with interactive toys.

Q. How do I desensitize my dog to squirrels and stray cats in the neighborhood?
ANSWER : A. It depends on the goal that you have in mind. I am going to assume that you would prefer that your dog not chase squirrels or stray cats in the yard/street. In this case, your options include: (1) training your dog on a “Leave it ” cue using positive reinforcement methods, (2) training your dog not to pull on its leash when it sees a squirrel/stray cat, and (3) training your dog to perform a more desirable behavior when it sees a squirrel/cat.
Training your dog on a cued “leave it” command is useful because it will give you the ability to tell your dog to stay away from any number of undesirable objects on your command. Training your dog to perform a more desireable behavior when it sees a squirrel or cat will substitute a behavior you find acceptable (sitting, laying down, coming to the door, etc.) with a behavior you dislike. Your dog can still react, just in a positive way. If your dog pulls on the leash every time you see a squirrel/cat, training not to pull will make your walk safer and more pleasant.
The ideal training method to use with dogs, or any animal for that matter, is positive reinforcement training, particularly a method called “clicker- training.” The basic concept of positive reinforcement training is to pair a reward (reinforcement) with a behavior you want to increase in frequency. In other words, when your dog performs the behavior you desire, it receives an award, which reinforces the desired behavior so you get more of that behavior. There are many excellent books in stores or on-line that describe positive reinforcement training in detail and many give step-by-step instructions for training common commands like “leave it”. Look for books that specifically mention positive reinforcement training or clicker-training. You can also take dog training classes to learn the techniques, find a mentor who already uses clicker-training, or request a consult from one of the pet experts on this site to guide you.

Q. Why do dogs eat grass?
ANSWER : A. Some pet parents get concerned when they see their favorite canine nibbling on grass in the yard. They wonder whether it is because hunger, boredom or an indication of an underlying illness. Often the consumption of grass will result in vomiting because it irritates the stomach and gastrointestinal tract. This is an extremely common problem for dog parents. There is no one reason for why dogs exhibit these behaviors and it is very much dependent on each dog. Here are some of the reasons why our dogs choose to eat grass:

1. Nutritional Issues

Historically speaking, dogs are considered omnivores, which mean they consume a variety of both meat and plant-based food. There is some indication that dogs with a low fiber diet may choose to scavenge in the grass to fulfill this nutritional deficiency. These dogs may also find that grass has an appealing flavor and consistency. If you feel that this may be the reason for your beloved canine consuming grass then consider discussing with your veterinarian on how to incorporate more fiber into your dog’s diet.

2. Boredom

Many dogs who are not receiving adequate exercise will be become bored and search out activities to occupy their time, including eating grass. Evaluate how much exercise your dog is getting on a daily basis and consider more walks or other fun activities, such as playing fetch or tug of war.

3. Upset Stomach

There is a belief that dogs with an upset or gassy stomach will self-medicate by consuming grass. Vomiting often follows this grass eating activity eliminating the contents of the stomach or changing the gas distension within the gastrointestinal tract. However, there is not much scientific evidence to back up this theory. If you are concerned about too much gastric acid in your dog’s stomach or any other underlying medical issue that could be the reason for their grass eating, consult with your veterinarian.

Overall, grass eating is usually not toxic to your dogs unless your lawn contains chemicals, including pesticides or herbicides. Monitor your dog’s behavior along with his diet and exercise to determine if there is a reason for the inappropriate grass snacking.