I run a very similar surface to that myself. We use a big industrial vacuum to clean our track before the barriers go down, and my mi1 (which has no holes under the diff) is ALWAYS getting rocks wedged under the diff pulley. I've just recently cut out a space under the diff to prevent that, as none of the cars with holes under their diffs have this problem at our track. My tf5 rtr (not much left of the RTR part now..) will do many laps no probs with the track un prepaired. Best thing to do is get Robinson gears. Hardened pinions and the skinny spurs. Really really tough, I have never damaged the teeth on one of them.