http://www.llu.edu/llu/medicine/plastics/patient_info/dermabrasion.html  With illustration goodness.  According to that, after they use what's basically a sterilized Dremel to get the gravel and dirt out from the skin, it will take 6-12 months before you should get a good tan.  How does that fit into your plans? I just picked up some sweet under-pant sixsixone knee pads.  Between my helmet, armored gloves, textile jacket, knee pads, and shin-high race boots, the only thing that's unprotected is my hips.  I think about that Dremel every time I put my stuff on. As I always say in any gear thread, at the end of the day it's your life, and your decision.  All I can do is show you the door, you're the one that has to walk through it.