Unless the anemone cooperates (which they never do), remove the rock and suspend the rock over a bucket of water so the anemone dangles in the water. Secure the rock and go nurse a beer.
When you are done, the anemone will be in the water and you can put the rock back in the tank.
Although it may not look pleasant for the anemone, it is far safer than trying to peel the foot of a rock.