[DonRotolo]

We went with latex tubing that sticks out like a vacuum cleaner brush. It whacks the ball when you get close, putting backspin on it, letting the ball follow you backwards if you go slow enough. The roller is about 2/3 the height of the ball and spinning pretty fast. When the ball gets too close, the tubing folds against the roller and acts more like wedgetop tread on a cylinder.