This is why I will never have a large population of fish in a reef system.
With anchored live corals and such this can be a nightmare.
I have usually caught fish in a decorated display by removing all the rocks/decs from one end of the tank as required, then placing a large "bag net" in that corner. A bag net is a clear transport bag which has been inserted into a standard net frame (the net is removed completely from the frame, no netting!) You push the top edge of the bag up into the frame and roll/fold it back over the wire frame. Thus creating; the bag net.
Using a wooden dowel or other chase instrument, you "herd" the fish into the bag net, which never moves. It pays to observe the escape pattern of the fish; use discretion and strategically place the trap. Sometimes placing a little food into a clear mason jar or acrylic box will also work, you simply lure them into the trap and quickly cover the jar with a net. Patience required here; it usually fails the first few times.
