We use, depending on the size of the ball, the following.....terracotta planter pot overflow pans like the one Adam showed except ours have a side entrance chipped out and sanded down...dark blue plastic cereal bowls with side entrances cut out and for the bigger girls we found these great super heavy, thick black rubber bowls at the local feed/tack/farm supply store. Had to use heavy wire snips to put entrances in them though but they are great. I think they are used for bigger dog bowls or some such thing. I love our local farm supply store and the dollar store LOL!
~~Jo~~