The rocks are VERY stable. It would take getting knocked off the stand for the rocks to fall, and in that case I think I'll have bigger issues to worry about.
Regarding the sand, it seems like for every person that says its bad, there's a person that says its fine. Calcium supplementation should prevent them from eating the sand, too. That said, I may look into putting some tiles down instead. I won't be getting a leo for probably two months so I've got some time to experiment.