I'd say best bet is a BTA. When I placed ours, it almost stayed in the spot I placed it on the rock. It only moved a few inches. And when it split, the second simply moved to another rock at about the same height. My advice would be to place it as high as you can with decent flow. To be on the safe side, allow room for it to move--no neighboring corals--just in case it doesnt like the spot you've chosen. Ours hasnt moved as of yet, so I'm guessing they are happy. Oh yeah, and BTA's are the most accepted anemone by a variety of clownfish. Good luck and, I'm sure you've heard it before, make sure you have proper lighting and a stable system.
I dont think a Flame will be a problem. I would say IF it decided to sample the anemone, it will not do it again. And if your clowns host it, they will protect it. The only fish that gets close to our BTAs is a Coral Beauty, but shes the friend the clowns have--they chase everybody else when they feel like it.