Seems like most discussions of "durability" in tennis balls refers not just to the covering, but their ability to hold pressure, etc. I use a Ballsaver to keep my practice balls fresh - it really works if you open/close it every few days. What I'm finding, though, is that the fuzz wears off WAY before the ball itself wears out, so I end up with perfectly good, responsive balls with no fuzz, which makes it hard to practice high-spin shots. These are currently Penn Championship Extra-Duty Felt. Can anybody point me to a specific make/model of ball with fuzz that will last longer?