Lexane + duct tape, I've done that for my hero 3 silver and it works great.
EDIT: you can actually unscrew the case glass and replace it with lexane, you can skip using duct tape then but you lose the waterproof capability iirc.
I use the waterproof one that came with my go pro and have used black duct tape over it to A ) Hide the light and B ) give that added layer of protection.
Granted I have hardly used it in games, but it has taken some direct hits and has not cracked, and they are easily replaceable if it does break.