When I took the last anemone out of my tank I used the ice cube trick. The first attempt was an absolute failure. After a little more research I learned it takes many, many, many ice cubes. I think I went through around 18 regular ice cubes from the standard ice cube trays.
If you only tired one or two ice cubes try again and be persistent. Also, take the rock out of the water if you can, it will make it much easier.
Another thing is to get a soft bristle tooth brush and gently slide it against the foot. I would try the ice cube again if i were you. But, completely your call.