I have a Finnex 30M arriving this week and plan on chopping LR smooth on one side so I can attach it to the back plastic divider wall. I saw some threads on building a wall with egg crate, rock and foam, but I do not want to use foam or egg crate. I just want to stick a couple pieces to the wall and the rest of the rock on the bottom.
I was thinking that a 2 part epoxy might work. Have no idea what brand would be reef-safe?
Any suggestions?

http://www.bulkreefsupply.com/advanced_sea...amp;x=0&y=0

Lowe's sells some marine safe epoxy as well. I forget what its called :/

If epoxy adheres to acrylic (which I think it does) then it is probably your best bet.
For what it's worth, I had some anemone encrusted scallop shells that I wanted to attach securely to stone tile on the back wall of my tank. I drilled two small holes in each shell, and matching holes in the ceramic tile. Then I got a length of 3mm threaded nylon rod and some little nuts and washers. I cut the rod to appropriate lengths, put a nut on one end and melted the top of the nut a little, which had the affect of darkening it from white to brown/amber/black and making it look irregular, more like a bump on the shell than a white plastic nut. Then I just bolted the shells in. The hardware was cheap, the nuts are practically invisible, the shells are very secure, removable, and I didn't have to drain the tank or worry about any toxic chemicals from glue. For your project epoxy is probably easier, and even more invisible, but I wanted to mention my alternative to give others the idea.

For what its worth, those foam rock look alike backgrounds made by Hagen n such will look exactly the same in time. It'll cost ya less then 20 bucks and take ya maybe 5 min to put it. I've had em before and looked just like any other rock in my tank after about 6 months. As a bonus... They only 1/2" or so thick, your eggcrate alone would take up.