Is it at any point okay to have sand or dirt substrate for bearded dragons? Nazar will dig under the puppy pad in her tank and she seems to like being covered up when she sleeps, she has a washcloth in there now and if I cover her up at night she doesn't seem to want to dig as much? Could I get a Tupperware container of reptile sand for her to dig in for an hour or two out of the day or is sand completely off limits? Is there anything else I can give her to dig in?