I'd get rid of the dog - I had a dog that attacked other dogs, it was a pitbull. I worked really hard with her and an animal behaviorist to break the habit but it never happened completely. The problem wasn't her seeking out dogs to attack, but other dogs coming up to her. I always kept her on leash but she still managed to attack several dogs. Seems like no one wants to keep their retarded ass dogs on a leash so they would wander up, and I'm like "Hey get your dog, my dog is going to kill it in like 5 seconds" sometimes they'd hurry, usually not. Anyway, after like the 5th time it happened, including one time this stray dog just charged us and I'm pretty sure my dog killed it, she had to be put on a vicious dog list. There was like a $5,000 vet bill that luckily my home owners insurance covered for a dog that was roaming the neighborhood off leash and decided to come into our yard. Anyway, I put her to sleep and I'm glad I did. There was sooo much stress from owning that dog. I guess I could've muzzled her everywhere, but that seemed stupid. Loved people, great with cats, even my lizard and ferrets she was awesome with.
The point is, people are stupid with dogs, they will bring their "friendly" dogs out off leash, or even on leash and just walk em right up to your dog. Like stepping outside with a dog on leash is some sort of invitation for all the stupidest people in the world to walk up to you