Aggressive dogs are always aggressive because they are frightened, and want to defend themselves, not because they love to attack people. Therefore, almost always, when you show a little patience and understanding you can turn a very aggressive pooch into the friendliest, most peaceful animal in the world.
Just watch this video if you need any proof. Sunshine, the Chihuahua, was living in a shelter, and she was barking and growling at everyone, until one day a lady called Tammy appeared. The pooch felt her kindness, love and patience, and one hour later… Well, watch to see what happened one hour later.