We had a plain foam one in my mother's garden (LOTS of specimen plants and not wanting DSs to boot in next door too easily) BUT it did become completely waterlogged with each fish pond dip, hence drenched trousers. The ball's demise was at the teeth of the neighbour's puppy who converted the ball into confetti in the time it took to go over to collect it...!
SO what I would like is a foam ball coated in plasticky stuff to make it a bit more water resistant. Any ideas?