This afternoon I was riding single track in the snow and hit a rock with my Gary Fisher that ripped off my derailleur. Stripped the bolt hole in the frame too. This is the second time I've had a derailleur ripped off riding in the woods. First time a branch wedged in and tore the derailleur off and left me with a 2-3 mile walk. This time I was only only a half mile from home. Does anyone make a sturdy guard to protect the derailleur from stuff like this? Or has anyone come up with a do-it-yourself piece of gear?