If they are large, inject them with either a strong kalkwasser or pickling lime solution (1 tablespoon pickling lime to 2 tablespoons of water, mixed and microwaved for 30 seconds). Even a copperband will avoid the large ones. See
http://www.garf.org under aquarium pests for more details.
And, as usual, Guy is right on the difficulty of maintaining copperbands. The one that I have currently eats everything, but that is unusual for the species. Most want live food only and stress easily.