Egg Crate Under Rockwork ?

[viperfish]

a couple of inches of sand will cushion the rocks from creating any stress concentration on the glass. My only fear with eggcrate is that it's just another place to trap debris that can't be siphoned out and sand sifters won't be able to get to it. I guess it would help in the event of a rock slide but I've never heard of stationary rocks on a sandbed cracking glass.