One of my guinea pigs likes to burrow occasionally which isn't a big problem. I noticed that some people use bricks to weigh down the fleece. I bought a few today but noticed how rough and sharp the corners are. Considering they're about the height of a guinea pig's head, I'm rethinking using them since I'm afraid they could get hurt if they run into one. Any thoughts on that? I thought of filing down the corners but there's still the risk of them running into them.