I prefer mixtures over one solid substrate. I use a playsand, peat moss, and backyard dirt mixture for my SPL. Heat rocks I have never cared for. I use heat lights over boards for hot spots which heats the surface (belly temps) and the top of the lizard. Reptiles get impactions from improper temperature and humidity settings. The sand isn't a problem, but the keeper's husbandry practices are. It's one of those blame the animal or everything else but the actual problem (the keeper). The good thing is, once the problem is noticed (the keeper's husbandry mistakes) you can work on fixing the problem.