My hedgie falls out of his wheel a few times a night. I used to blame it on the wheel being too narrow (his old one was only 4" deep) but this one is a good 6", so I don't know what to do about it. I don't think he evens falls out, so much as a foot slips off the side and he face-plants. I thought about adding traction, but don't want this whole bloody feet issue. Anyone have any suggestions?