My foal used to chew everyone's tails. A baby thing I guess. But what really helped was keeping hay in front of them 24/7. That's something I never used to do, since hay is really expensive around here and I don't have pasture either. But I just make sure they always have a non-fattening grass hay in front of them and he quit chewing tails.
Buying some grass hay might be cheaper than fixing the fences. Worth a try anyway.
I bought jolly balls for the horses, they totally ignored them. So I gave them to the Berners and they love them. They have been outside through two winters, not a problem. Just don't run into them with the snowblower, they get pulled into the blades, then fly out when they can't be caught and land about 10 feet away....
I hung mine in my mares stall because she takes the halters off the wall! But she plays with it, this morning when I went out she was swniging it around. Never had experience with them outside, though, but I would think they are durable!