Agree with Alexcyf, I used a quarantine box with sliding side panel, I held the door up with a clothing peg. Larger the box the better. Leave it there for some time, feeding only via the top of the box. Once the fish starts coming in to feed, wait for a good opportunity to release the door. I've caught anthias, cromis, clowns through this method.
I have to admit, it takes plenty of patience, but u wont destroy ur scape trying to catch the fish with a net.