Before I adopted Jerome he was a happy, easy going dog that attended the doggy daycare facility I had just started working at. He got along well with all other dogs of all sizes. Then came a small dog with big attitude named Hercules. Hercules had an issue with other dogs. If they got too excited, played too rough, moved too quickly, etc he would run behind them nipping their back legs. This behavior occurred over the course of a couple days as Hercules was boarding with us but in decreasing occurrences. One day the pack got very excited as it was towards the end of the day and a lot of dogs were getting picked up. Hercules targeted Jerome for his nipping behavior. He bit Jerome's hind leg and Jerome had enough. He turned on the dog and really went after him. After this incident Jerome's behavior changed. Anytime the pack would get really excited, Jerome would immediately run to the fences (the daycare was divided into three sections with vinyl privacy fencing) and start fence fighting. He didn't go after the dogs in his run, but it was always a great fear. Skip ahead a couple months and Jerome's behavior hasn't improved, but I have adopted him and neither of us is still with the daycare. He is getting plenty of exercise and lives at home with two other dogs (one larger and one much smaller than him). He gets on perfectly with them and never triggers when his little brother barks, growls, plays rough, etc. The issue though: anytime we are out and Jerome hears a smaller dog barking he goes into fight mode. Pulling on the leash, barking, growling, the whole nine yards. I have a very hard time calming him down and getting his focus back. For the immediate time after it seems that he sees anything outside of his family as a threat. Please help!