he uses dirt. you'll hear a lot about it on pro exotics' website under uro care or uro faq or soemthing. It basically links you back to old posts on here. I'm fairly satisfied with my little dirt setup after a little bit of toying with it. I only have about 3-4" of dirt in the highest part in my tank, but I found ways to compensate for that lack of a deep layer by putting things in she can burrow very far under (like an extended bottom of a retes stack submerged in the dirt so only the top is showing). In my limited experience with it, it seems like uros simply love to have a hiding spot where they can get out of sight and reach, which is something standard hidespots can't provide. With my setup I can technically reach her if I lift the stack thing, which I like because it's convenient if I have to get to her for some reason. They also benefit from the humdity. My uro is not a good shedder, mainly because of the scars on her back from an awful experience she had with a past owner involving a high wattage light bulb, and with the added humidity in her fake burrow, she is shedding better.
Good luck.