No, unfortunately, they cannot be glued without killing them. First of all, lets see a list of tank setup, inhabitants, and all testable water parameters (all numbers for parameters, please). Generally, when an anemone completely detaches, it is quite unhappy with the tank in general, usually suggesting a water quality or environmental problem. As far as powerheads are concerned, you can either place a sponge on the intake or make an enlarged enclosure around the intake.