There's no way to get my rock out without a total do-over, so I have been smothering any pest anemone with kalk paste. I'll keep doing that until I get fish and a bristle tail file is at the top of the list.
The kalk paste seems 100% effective but leaves quite a white skid mark. After a week or two, I scrub at it with a tooth brush and it's almost all gone. I'll put up with having to scrub at the skid mark because the paste is easy, effective and inexpensive.