I appreciate this dilemma. Rock crawling is a blast, and fenders tend to get sacrificed. Of the research I have done, two things have risen to the top:
1 - Stock fenders can bend under pressure, thus saving your quarter panel. Aftermarket fenders, including carbon fiber, will not
2—To avoid hitting fenders, embrace tire poke. I have heard many cry out about the adverse effects of tire poke, but honestly, I have had many offroad vehicles, and none have had any serious impacts of tire poke as long as you keep it reasonable. When crawling, the tire will keep the fender a few inches away from the obstacle. I plan on running 38x13.5x18 tires with a 2" lift and -12 mm offset (forged Racelines). I have a friend who is running a similar setup, he is substantially hardcore, and he has retained his fenders.