I got this idea from some fish keeping forums I've read and figured it's be perfect for my BP...
I plan on taking a polystyrene block and carve it down into a rock background with a hide on each side. I will then paint it with Krylon Make it Stone paint and then go over than with a clear nontoxic sealant.
I will probably use a 5" thick block cut to fit the back wall tightly. Then in front of that block carve a couple hides out of 12" cube blocks. The whole thing will be put together to look like 1 big piece.