My 14 year old flat-coated retreiver that we rescued from the SPCA, she had been there for 6 months due to her not being a puppy and also because she was (and is still) "aggresive". This caused soooooo much trouble because we couldn't do the normal fun things with her like going to a friend's house and letting the dogs play together etc. The neighbour hood bully was and is afraid of her. But anyway, we ended up getting fed up and decided to take action! We asked a friend that had a dog of similar size and strength, put them on leashes and brought them outside. My dog (sam) was instantly rigid and she definatly wanted to fight where all the other dog wanted to do was play. we put a muzzle on her (as she is a big and not-so-delicate dog) we then let the other dog close to her and after a couple of minutes went for a walk. after awhile she calmed down a bit so we took off the muzzle (if you just have a small dog you probably would not use a muzzle) and gave her some treats. After a couple "sessions" she was good with that dog but unfortunatly it does take her a bit to settle down around new dogs. But about 2 years ago i was sitting in the house when i noticed another dog in our yard (no idea how it got there
) but she ran u[p to greet it and they ran around playing so maybe it was just her seeing the other dog(s) as a threat to me? Anyway, Good luck with your dog!