For hard coral and zoo's I just use super glue gel. Walmart has it usually in a 2 pack pretty cheap. Just make sure it's gel. When mounting a sps for example I put a dab on the mounting piece position the coral and put my hand in some saltwater and let the drips off my hand hit the glue, it will turn a whitish color and harden enough to keep it still, then I put it in the tank.