The only way he will relax is if he knows you will protect him in all situations. That way he can differ to you when that happens so you don't backslide on all of the hard work you have put in with him. I know it's easy for me to say, as I am a large guy that would not hesitate to square up with a large individual dog while putting my dog behind me. I would suggest jogging with pepper spray, and if any dogs run at you let them have it. If animal control is non existent around there and the guy seemed decent last time, I'd go talk to him and give him fair warning about what happened while saying next time you will need to protect yourself and your dog.