Amazingly well behaved Dog shows aggression to only ONE specific other dog
So I have a 2 year old Black Lab - Flat Coated Retriever mix that I brought home from the SPCA about a year ago. He is the most well behaved dog, and I don't just say that because he's my dog, but everyone including the vets, friends, other dog owners and dog haters alike all tell me what a fabulous dog he is blah blah blah... He's really great with other dogs, no matter where he is, our backyard, other backyards, dog park, pathways, anywhere, anysize or breed of dog. He'll even make himself smaller when he plays with our neighbor's small toy dog. Oh and he essentially never barks.
Now recently, over the past few months there's this one dalmatian he shows aggression towards. I've never ever seen him show aggression within the year I've had him home. But for whatever reason this Dalmatian freaks him out or something. It's always running with his owner on the bike. The most frustrating thing is I wasn't with him when he had the first encounter. So I don't know what may have set off an initial bad impression.
Anyhow, it's getting annoying because it's so random coming from a dog like him. When we talk about it with friends and other dog owners they don't believe us, that he's ever act like that.
We've done training with him to ensure we've established a leadership/dominant role and that he's not trying to protect us. He walks beautifully on the short leash and responds to every command, and then he just looses it as soon as the other dog comes by.
You must get the point now, and I would expect this happens with other dogs as well. What I want to know is how to train this behavior out of him. Now we have to worry about letting him play off leash with the other community dogs just in case his arch nemesis comes by.