Never heard of anyone using stones as substrate but i guess it could work? Just make sure your snake never eats one... As far as the heat rock... whats the point? Your snake isnt going to coil up ontop of the rock after a meal to help digest so really theyre kind of pointless for snakes IMO... UTH are used to help with digestion and provide a nice warm spot for your snake... A heat rock serves no real purpose for a snake.