I have this same problem with Truman when he goes in his crate at night or for an extended period of time - I line it with a puppy pad in case of an accident that typically ended up shredded in a corner.
Why they do not make them with adhesive on the back, I will never understand but I bought a cheap pack of panty liners and stuck the puppy pad to the bottom of the crate (or floor) with the panty liners, with a strip of packing tape on the bottom for a little extra adhesion. The panty liners are as absorbent as the pad and hold it in place nicely.
I know it sounds odd but it really works - Truman stopped trying to dig his up!