I've also had good luck by 'net training' the fish. Use a favorite food, such as frozen or live brine, place it in the back of a big net and allow the fish to eat from it for a couple of days. They will get used to the net, associate it with food, and then after a few days, when the unsuspecting critter swims in, you can net him out.
I've also used the drain/fill method for bigger critters.... it' hard to use that one with lots of live rock and a skittish dottyback!
Good luck,
-Rob