I had one under my salt water dish which was also pressed into the sand for easier access and I moved the dish over some only to find him once again under the dish. He tunneled over to it!
So, from that time on I just gently replaced the dish over him each time and he was perfectly fine. I believe it made him feel more secure to have something completely blocking his entrance, who knows?.
It is scary to think you'll possibly cave a tunnel in, so others may have different advice for you. Good Luck! Oh, I almost forgot- I also misted lightly where he was.