I read this interesting article stating that confrontational or aversive methods does not help training aggressive pets. "Veterinary researchers have found that most of these animals will continue to be aggressive unless training techniques are modified."
Territory and fear are the two common factors for aggression:
- Territorial aggression – It is directed towards approaching people or animals outside the pack in defence of the dog’s area (yard, room or home), or pack members. Sometimes, it's due to resource guarding. For example, the dog may guard his food, toys, water, kennel or people - if the dog think that person is his.
- Fear induced aggression – It occurs when animals or people approach a fearful dog. It is most common when the dog finds it difficult to escape. Unpredictable children could also trigger such form of aggression.
Certain medical reason could also be the reason behind the aggressiveness of a dog (source: http://www.petplace.com/dogs/aggression-in-dogs/page1.aspx). For example, dogs having neck pain often display aggression when they are pulled by the collar.
The best approach is to consult your vet, a professional dog trainer or dog behaviourist.
