here's one of the rose bubbles i've kept. no rock under him. he stayed at the base of the rock work touching the sand. as a matter of fact, his foot was connected to the bottom of the tank.
here's a maroon with another rbta, also on the sand bed. same thing- foot attached to the bottom pane of the tank.
anemones don't typically emit slime. it's definitely a sign of stress.
i've kept a couple hundred anemones of various types. some for a couple weeks, some for a year. some of them move multiple times, and some of them will stay in the same place for 6 months then move. i really don't think it's the kind of thing that you can count on.