Re: New to the hobby and the site
Epoxy putty is a great product; I've used it a lot in reefs. It doesn't 'stick' so much as it 'locks up', kind of like wall plaster sticks to the lath behind it by squishing through the spaces and forming 'keys' that harden in place. So rocks with lots of little pits and irregularities are bonded very securely, but smooth rocks not so much. If you use epoxy putty, be sure to glop putty in between two rock surfaces that have 'holds' like rock holds in rock climbing -- a place for your fingers to grab. The putty solidifies and locks the two pieces together.
Silicone adhesive/caulk is strong and cheap and effective, too. I've not used is on rocks, but if your rocks are smooth it might be worth a try. That's the route I'd go, but I usually have a good supply of silicone around. Be sure to get the 'aquarium safe' kind.
I think I could turn and live with animals, they are so placid and self-contain'd.