that's too bad... I can't believe they threatened you and Rex! did you tell that to the policeman? It's just a stupid ball...

I advise you to not allow Rex off-leash in public areas like that. It is too costly to you, and yes, some one might try to hurt him. Look for fenced-in parks allowing dogs, or open fields away from a lot of traffic and people. I have played with Gonzo on a dog-friendly soccer area, and when kids come to play soccer I just leave or play with him on-leash. It's kind of asking for trouble, IMHO.