Live sand and Live rock

Question
hey Paul.
Is it true that when you stack live rock on sand it is like a time bomb? It makes sense, if the sand shifts because of a fish or weight, the rocks could tumble. How can I prevent this?

Answer
my rock has always gone in before sand for this reason, i stack it on the glass and make sure its stable (may use miliput for this) or you can get something called egg crate to line the bottom of the tank. its plastic sheet with square holes through it (have a butchers on e-bay)