This has happened on a few occasions already at the dog park where, Sam, my 12 month old male GSD (not fixed), aggressively attacked another younger male dogs and/ or puppies. They would just sniff each other at first and then suddenly Sam's hackles stand up, he growls and then lunges himself at the younger pup. He gets taken to the dog park on a regular basis, like almost everyday, and he does fine with other dogs big and small, so I don't know why he only targets younger dogs/ pups. Does anyone know why he is doing this or know how to correct his behavior? I am getting him neutered soon hoping he'll stop his aggressive ways afterward.