yes rip out every rock in the whole tank, then catch the fish. Being serious though damselfish are impossible to catch, maybe a trap but they are skittish about traps.
I’m not sure what all you have in there livestock wise. As a last resort, when you’ve tried everything in the book to catch a particular fish or multiple. I just drain the tank. down to a few inches. I’ve done this in the past several times and it works well for those fish that don’t like to hide in the rocks. It does take a decent size pump and enough trash cans to hold most of the water. Drain quickly, catch fish, pump water back in. Depending on your rockwork, this may or may not be an option. Not sure what other livestock you have in there. Coral will be fine for a bit out of water. This hole process shouldn’t tank any longer than 30 minutes or so. Not ideal, but has worked for me as a last resort. I’d never thought of this until browsing on wetwebmedia 15-20 years ago. I can’t remember if was Bob Fenner, Anthony Calfo, Steven Pro, or another staff member that mentioned it. I’m thinking it was Anthony Calfo though. Lol. I’m curious as to what type damsels?