OK, after reading the post about the guy who kept crashing into his chainguide and rotating it, i thought about the possibility of making a floating lower roller. Basically it would be kept in place by chain tension pushing it down, but when a rock hits it hard enough it would rotate up and out of harm's way. The biggest issue I can think of would be keeping it stiff enough to do its job while allowing for motion, and it if it a dual ring system preventing it from rotating when it's not supposed to. Anyway, it's just an idea...