1. First, are you the one who starts the aggression and then your dog simply joins in?
2. And second, does your dog listen to you just before the aggressive behavior starts when you are trying to express to him that you disapprove of the aggression?
At the point when your dog starts the aggressive behavior, he is not listening to a word you say or acknowledging your displeasure. He is making his own decisions at that critical point and will not listen to any command from you for him to change his behavior. He is acting from instinct and his instinct tells him that the aggression is necessary to protect his pack and his own life.
There is a wide range of aggression from dominant to fear and everything in between. Some aggression occurs on a consistent basis and then there is aggression which erratic and unpredictable. You must take notice of what sparks your dogs aggressive behavior. Is it certain situations, people, animals or other dogs, or objects such as cars or bikes.
The way to stop dog aggression is based on the same factor that is causing the aggression. Again, your dog sees himself instinctively as the pack leader. If something causes him to become fearful, he will instinctively attack what is causing his fear in order to protect you and himself. More dominant dogs will act early, often attacking when they still have the option of fleeing. A less dominant fearful dog will only attack if they have no way to flee.
The key to stopping the dog aggression is to show your dog from the beginning that you are the pack leader. In fact, this is the most important key to any type of dog training. He must see you as the pack leader when you are with him in your home. You must first establish this in the home before you can expect your dog to see you as the pack leader during the walk. Cesar Millan, the Dog Whisperer, says that during the walk, it is very important to walk in front of your dog to show him you are the pack leader.
There are a number of great videos on the web that show you how to stop dog aggression by establishing yourself as the pack leader. Once you have established that you are the pack leader, and a situation arises that used to make your dog aggressive, he will instead stand back and observe how you deal with the situation. If you are not fearful or intimidated by the situation, he will not feel the instinct to attack. Remember to always be consistent and soon you will see less and less of the aggressive behavior.