An aggressive dog can be a very dangerous animal to have around. The signs of aggression may be teeth showing, ears back, snarling, biting towards people or other dogs. The first and biggest step in aggressive dog training is to recognize the reasoning of the aggression and deal with that issue directly. Luckily most of the time you can train a dog to get past fears and aggression.
There could be abuse of some kind behind a dog’s aggression. Possibly physical abuse, abusive training methods, keeping a dog confined, under feeding or teasing can all be causes of aggression in a dog.
Some dogs were bred for their aggression (Pit Bulls, Rottweilers, etc) and the aggression may be a genetic trait. Also the dog may have been trained to be aggressive. One other reason for aggressive behavior is fear of the unknown.
Medical reasons may also be behind the aggression. A thorough examination by a veterinarian will rule out this reasoning quickly.
The dog may also think they are the alpha leader in the home pack and establishing dog dominance over other animals or humans. You must maintain that you are the alpha leader not the dog. This is called Dominate aggression.
Aggressive dogs normally give warning signs before aggressive behavior turns into action. Growling, barking, showing teeth, head and ear gestures can all be warning signs of aggression. Punishing the dog while they are in the frame of mind that put them in the aggressive state may train the dog to leave out the warning signs and go straight for the bite.
You must get a handle on aggressive behavior right away as there is safety for strangers and family members that is the number one concern. It is essential if you are raising a puppy to get them to understand that aggressive behavior is unacceptable. Socialization of a puppy through six months of age is one of the main focuses on training against aggressive behavior. Fighting or tug games should be avoided as they will encourage rough play or aggression as acceptable. You should know by the time the puppies is in teething whether they will continue biting or they will learn a soft mouthing. Retrievers are infamous for exhibiting the soft mouth as they retrieve game.
If you have an older dog you will want to practice some counter conditioning where positive feedback is given to the dog that shows non-aggressive behavior in situations that would normally cause a bout of aggression.
If you cannot get a handle on the aggression issue in a timely fashion it is recommended that you bring in a professional trainer. There are legal ramifications that can come about if your dog bites someone. Do not fool around with an aggressive dog. Bring in the help of a professional if you need it and do not spend too much time trying to train yourself if it is a full grown dog.