Boy that is a tough situation. Like you said you have to watch out for your own personal safety.

Can you contact the town? I don't know if they can do something about it or not.
Or even ask them if they or you can post a sign in the park, saying something along the lines "please be nice to your dog we can see you".

How far away is animal control? Are they close enough that if you call them when you see it happen that they can get there in time to catch the person?

Other than those I can't think of any other things you could do that would not jepordize the safetly of you & your dog.

I hope someone else may have some more info for you.

I wish you the best of luck!