Despite the warnings about not using sand as a substrate for Leopard Geckos, there are still people that house their Leos on sand. I have even seen pet stores with baby leopard geckos on a sand substrate.
Here is a link to a site with some graphic images of what can happen when a leopard gecko is allowed to ingest sand.
Warning: some of the images are unpleasant, however, I feel it is important that you see what can happen to a healthy gecko that is housed on sand.