You may already know this, but in case you didn't, you can build a fish trap using a pepsi/coke plastic bottle. Cut off the top 1/4 and invert it towards the rest of the bottle to form a funnel into it, then bait it. That one didn't work for me, or I wasn't patient enough,so I also bought an acrylic trap on amazon. I caught 2 of my problem damsels within 10 min when they went in together with a tang. The 3rd damsel is refusing to go in even after a few days, so my trap is patiently waiting inside the tank with rocks in it to disguise it until he gets used to it and makes a mistake.