Use superglue GEL. Make sure it's the gel kind though or else it will be impossible to keep the zoas in place. Take the zoas, dry the spot off where you are gluing both on the rock and on the zoa, apply superglue gel and wait till the glue dries enough so the zoas don't fly off in the current. Remember, zoas are very hardy and can stay out of the water for a while.
Good luck.