Its a shame to see dogs ruined by poor handling and training, i have had to defend myself against dog attacks a couple times and i never blame the animal. Its a tough pill but if you are breaking the rules by leaving the dog off a leash in a leash area than you are in a pickle.
Either walk the dog on a leash and do what is necessary to protect yourself and your animal.
Or bite the bullet and go elsewhere away from the problem animal.
Unfortunatly you cant fix stupid and it sounds like you are up against plenty of it.
Good luck, i hope you avoid further confrontation.