Our dog is like this. He will only socialize with our other dog. All other dogs he attacks. The vet said he has fear aggression. We have had him since he was a puppy and have loved him and never miss treated him. We now ensure he doesn't get into situations that spark the aggression, so we don't take him off the lead or out with other dogs. He's 9 this year and we just make things easy for him itms?