Hi All, Boots is about 6 now, and I'm trying to figure out what is causing one of his few issues. Basically, he seems to be fear/aggressive with mostly puppies and adolescent dogs that are too friendy. He was socialized like crazy for the first several years of life, with 1-3 hrs a day at the local dog park, with no issues. Never saw any negative interaction with puppies which would could have been pinpointed as a cause/trigger. Both my sisters have recently gotten second dogs. Sister1 has a 4 y.o. St. Bernard, and Boots has no problem with her, nor usually with large dogs. She recently got a 6 m.o. French BD male that is quite the boy-man rocket racer type. From the get go I could see Boots wasn't real happy to be in the same area with him, and he actually avoided coming into the same room with the BD and us. Sister2 has a 5 y.o. Border Coller/Lab/Ausi mix, who both would wrestle all day if we allowed them. She also recently got a GSD/Border Collie/Lab female mix who is also loving puppy rocket. Boots is also not happy with her, however if I hold the puppy, he will come up and sniff her behind. Same behavior though, actively avoids the puppy. I know I failed by not addressing this years ago, however spilt milk and all that. Any suggestions on either DIY training, or specific Behaviorist type of trainer I should look into? I'm not sure, however I think it is important to note that he is not being typically dog aggressive as in approaching another dog and asserting himself or being dominating. He is one of those rare dogs who never really got into running to the gate at the park to see who the new dog was, unless it was one of his friends. Really loves friends, and never had complaint one from the local doggy daycare. Have had some people say its possible jealousy, however pretty sure if I left him with Sisters1 or 2, it would be the same.