Building a cave?

[SinfulSlave]

I am starting another salt tank, I remember reading in a marine aquarium book that there is some sort of adhesive that you can use to help make a cave out of seperate rocks. I am planning to use several small pices of black obsidian to make a small cave... however I cannot remember what kind of adhesive they recommended. I dont want to have to trust the guy at Home Depot about what may or may not be safe for my fish.
If anyone can help, I would appreciate it, and any other tips for making sweet decorations is welcome!
Thanks
Sin

 

[jamal-188]

There is a special brand called Aqua Stick and a couple others I believe, should be able to purchase it at your LFS or online.

 

[reefrunner69]

When I use an epoxy...I use Z-spar marine, you can get it at Home Depot or other home improvement stores.