I've done a rock wall as well. I zip tied the rocks to the egg crate and ensured my foam covered the zip ties. Held very securely.
One word of warning: Do not have any urchins if you have a rock wall. They actually tear the nice finished layer of epoxy coated sand off the front and expose the interior of the foam, which is not pretty and doesn't like to let coralline algae grow.
Didn't seem to be. I had 2 full size pencil urchins, and I swear they lived on eating the foam. Maybe it's just the pencils. If your tuxedos are not damaging it, then that's fantastic.
I didn't use Gorilla Glue, I used a different 2-part epoxy. Maybe that was my problem. Guess I'd better build another tank!
Come see minei even have supplies i can donate as well as techniques.
I use gorilla glue as final coat. I also have urchin. No issues
Ill take you up on that offer very soon. Ill also need your advice on how to build the stand for my Solana.