I went to the local plastics store today, and they have Pour-On high gloss epoxy. It's the stuff used to make thick glossy coverings on wooden plaques and so forth. Anyhow, talking to the guy there, he said it would stick well to glass and acrylic, and I could mix in a bunch of sand. After I poured the mixture in the bottom of the tank, smooth it out with a stick, I could then lightly sprinkle sand on top. Or, don't mix in any sand and just sprinkle the sand on top.
I bought a small kit, so I may try it on a small tank tonight.
Matt
http://www.eti-usa.com/consum/envtex/envlite.htm