I use this (http://m.lowes.com/pd/PLASKOLITE-7-85-sq-ft-Louvered-Ceiling-Light-Panel-Common-24-in-x-48-in-Actual-47-75-in-x-23-75-in/3280904) to put on the bare bottom of my tank and stack the rocks on that then put the sand in so they can dig all they want and it won't create a rockslide. If...