Eggcrate and 2 inches of sand to cover it.

my rock sits directly on the glass, and i filled a very thin layer of crushed coral in front and sides,,,not a fan of b/b, but nothing under the rock!

Most of my rocks were on the sand. My Engineer Goby has pushed most of the sand to the front and around the rocks. He likes lots of swimming room behind the rocks. I estimate that I have aprx. 70lbs of rock.