The form that treatment for dog aggression takes depends on the underlying cause of the aggression, and an accurate diagnosis is therefore essential. Most reputable trainers will recommend that a dog has a vet check to screen for medical changes that may be the cause of the dog aggression before attempting any form of behavioural modification.

Dogs that are aggressive from fear can be that way either from genetic predisposition ("weak nerves"), or from a traumatic experience. With these dogs, a programme of gradual desensitisation is often used in order to reduce the dog's reactivity to other dogs. The fearful dog may be praised or rewarded for non-aggressive behaviour, with bad behaviour being ignored.

However, there are some behavourists who rehabilitate dogs in a more direct, and dominant approach (see Cesar Millan) which involves a three step process:

• By exercising the dog first, so as to lose its energy and make it easier to handle
• Then, apply discipline to the dog; that is, instead of ignoring bad behaviour and rewarding the good, the dog behaviourist would simply punish or correct the bad behaviour before it is allowed to escalate. Also, part of the discipline involves establishing to the dog that the owner is the dominant one and the leader. For example, before engaging in a walk, the owner may open the door but wait until the dog sits and shows signs of being calm and submissive. Then, the owner proceeds out the door -- the owner is the one who leads, not the dog.
• The third step, after exercising and discipline (the discipline depends on the source of the aggression), is affection; although, only shown at the right time (when the dog shows signs of being calm, and submissive). So, this new approach to correcting dog aggression is not simply to ignore the bad and reward the good, but to establish dominance and to correct and sometimes punish the "bad", and to reward the good (although the latter is less stressed upon).

Dominance

True dominance based dog aggression is less common than fear aggression. Dominance aggression is influenced by several factors. Male dogs (especially entire males) are more likely to display this type of aggression than female dogs are, and several terrier breeds are particularly prone to developing this type of aggression. Dogs with mild dominance aggression may respond to the same treatment as fear aggressive dogs. However, dogs with moderate to severe dominance aggression will find fighting too rewarding to be fully rehabilitated. With these dogs, trainers may resort to the use of punishment in order to make the aggressive behaviour less appealing, or exploit the use of a dog's other drives in order to keep the dog's attention in the presence of other dogs.

Some believe extremely rank aggressive dogs may have to spend their lives separated from other dogs. However, there are many behaviourists who believe no dog is impossible to be rehabilitated; but the process requires a great understanding of dog psychology. Older dogs are harder to rehabilitate. A common misconception is that some dogs can never be rehabillitated, and must be put down. Because dogs react, and do not rationalize, they are able to move on much faster than humans; in extreme cases of aggression, it takes much more time and patience to correct, but it is still possible, as long as the rehabillitation process is effective and done routinely.