You’ve learned to defend yourself against rocks much the same way your giant ancestors do.
Benefit: You can catch an incoming rock. Once per round, when you would normally be hit by a rock of your size or smaller, or projectile of similar shape, you can make a reflex save to try and catch it. The DC is 15 for a rock two sizes smaller than you, 20 for a rock one size smaller than you, or 25 for a rock of your size. If successful, you’re now holding the rock, and if it’s of the appropriate size, you can throw it back, or simply drop it as a fee action. You must be aware of the incoming rock in order to attempt to catch it.