Having been the hobby for some time, it’s remarkable how many different types of “glues” I have learned to use. I've tried cyano acrylate, silicone glue, plastic epoxy, PCV cement, acrylic adhesive and two-part epoxies.

Two Little Fishies AquaStik is a two-party epoxy and among the handy glues I've tested. It is great for attaching corals, attaching gorgonians and for gluing rock structures together or holding pieces in place.

Another particularly useful way to apply two-party epoxy that I've discovered is to mold it into barriers to prevent corals from growing into each other.

The Red Coralline-colored AquaStick epoxy putty from Two Litte Fishies.
The AquaStik comes packaged conveniently inside a tube. Just pop the cap off to pull the epoxy out. Cut off a portion and begin to kneed the two-part epoxy together thoroughly between your fingers (which should take about 30 seconds). The epoxy will heat up slightly and gradually harden.

You have about 5 minutes of working time, so take your time getting pieces exactly where you want them. It's important to note the epoxy is not sticky—it will not ‘glue’ pieces together. Instead, the epoxy is like a clay that hardens: try to work it into crevices so there is more the epoxy can hold on to.

Strips of epoxy helps this rapidly-growing Monti from growing over other corals.
To use as a barrier, simply roll the epoxy into a round strip. Press the epoxy down along the edges of the coral. The coral will grow on to the epoxy strip instead of further encrusting the live rock. You can then break the epoxy off and replace it with a new strip of epoxy to prevent further spreading. The broken off pieces can then be attached to plugs/discs to create new frags that you can grow out and trade.

The "sandwich" method works great to attach frags!
For mounting smaller frags, a popular method is the “sandwich” method.

Roll a small ball of epoxy then apply some coral glue (cyano acrylate) on the top and bottom of the epoxy. Place your “sandwich” on the bottom of the frag then attach the frag to your live rock.  The epoxy will mold to the shape of the live rock and the coral glue will help hold everything together.

Epoxy is particularly effective for attaching corals to contoured surfaces.
The AquaStik has held up the “Bonsai” column in my reef aquarium amazingly well. Previous efforts to support the column by strategically wedging pieces of rock together were futile. The structure is now rock-solid and the pink color of the epoxy helps it better blend into the rock work.

AquaStik Epoxy does a great job holding up my "bonsai" rock structure!
One small caveat is that using too much epoxy at one time does make your protein skimmer over foam for a few hours.

With its many uses, the AquaStik Epoxy is extremely handy and convenient. It is definitely a great glue to learn to use and have in your aquarium supplies cabinet!