Live rock on eggcrate, sand or on bottom?

[Reef Pilot]

Reminds me last year when I was installing a new light fixture for a bathroom. It was on a full wall mirror, and got the old one off, no problem, and the new one fitted on nicely. But then I was tightening (just one more little bit of a turn) up the rear back plate that was against the mirror through a drilled hole to the wall,...I heard this horrible snap, and a big crack ran out from under the back plate.

Had to pull off the whole mirror which was glued to the wall, piece by piece, and using a hammer to break more pieces to get it off.

That was not a good day....