I had the same problem with a male krib. That little *%&# would sneak into any nook or cranny he could find, and even when I took nearly everything out, he would blend in with the gravel and practically disappear. Plus, it stressed out all my other fish. Big mess.
I broke down and bought UltraLife's The Trap 3x9, which worked awesome. I put a cube of Formula One in there and forgot about it for about 2 hours. Then I just sat down for about 10 minutes to watch the fish, and the krib I wanted to catch just slid right in. I dropped the door, and poof! He was outta there!
You can make a DIY version by using a 2 liter soda bottle or a larger Gatorade bottle with the wide mouth. Just cut the top off where it curves and then invert the top so that the mouth of the bottle points into the bottle. You can secure it with tape or something (I found it was hard to keep in place if it wasn't, I just gave up). The downside is that you can't close the opening once you get your fish, but they do find it hard to find once they are in there.