With the FN (flat pan), I've had great luck with binder clips. When I had the Martin's, and now, with my other SuperPet cage (cages with deep pans that you put the cage into), I put fabric down and then put the cage in. My smaller SP's, though, I'm at a loss with, as the cage fits right into the top of the pan!
My boys still try, but I have better luck then when I just put it down and crossed my fingers.
What kind of a cage are you using?