For me, I got TR ocellaris clowns. They come running up for a snack any time I get close to the tank. I can hand feed them. Way back when I had one in the JBJ 12 gallon with an orchid dottyback, if I forgot to feed them, the clown would jump into the back sump area. I assume the dottyback was the cause. To get him out, I'd place a small plastic cup in the sump - he'd jump right in expecting me to dump him back in the main tank, then look for a snack. Your clowns are obviously uncultured, untrained heathens.
I've read here that aiming a powerhead at an anemone's foot will encourage it to let go. I've never tried it. I wouldn't want to pull one off.