Rock anemones don't host
Personally i have 3 btas and a sabea (my clowns only host the sabea)
The things you learn once you have a anemone for example, btas will only move if they are uncomfortable (and maybe when they split which is not often at all) so depending on where you get it (if you buy it from a fellow reefer (very recommended) and your lighting is simular then setting it in a rock crevice will be enough) (if you buy it online or a lfs (not so recommend ) then it will move to shade in the beginning then slowly come out),
I love how some people make them sound like big giants that will trample your whole reef and kill all your corals this is so far from the truth, as someone mentioned before you will only kill corals if its touching it for a couple days, just keep a eye on it and the only issue you may have is if selects a cave/ledge and it retreats into the cave for some shade and you have a coral on top of that ledge (you will have to move that coral so it doesn't get stung)
They do not like flat surfaces they like crevices and ledges/caves,
I don't recommend you buying it from a lfs or online (except maybe maybe divers den) because anemones can easily be damaged either the foot or dying online you never know what your getting and lfs usually have sic stuff (in my area thats how it is for years i learned the best way is online or a fellow reefer that is active in the hobby not shutting down a tank) only really experienced reefers can take care of them (in separate systems with medication etc) if a anemone is sic or looks even a little bad DO NOT PUT IT IN YOUR TANK give it away or whatever, it will most probably die and not so good for your tank,
If they do die they won't nuke your system (so fast) you will see it dying over 2-3 days, you just need to pull it out before it decays and floats all over your tank
Getting a anemone off a rock is easy but like catching a fish or anything in our tanks it takes patience, with a anemone you bother it until it lets go, if its new it will let go in a couple of minutes, if its settled it may take a couple of hours or days of bothering it randomly