Bentley was really bad about growling and barking at dogs and strangers. Even leaves that rolled across the street. Our trainer told us to turn and walk away when he does that because barking is his reward. Once I started doing this and getting him out and about more it quickly got much better. He is almost 10 months. He is still learning but has come so far. He was ferocious before. Nipping and barking at dogs 100 pounds heavier than him. Right now, he is quietly sleeping in his bag next to me while I am getting a pedicure.
He now knows that not being nice will get him left at home. I hope I helped a little. Its so funny that they think they are so big and bad and then at home are cuddly as can be.