Lift the anemone out of the water, the rock must be above the anemone, so the gravity will drag the anemone down. I guess, you know that already.
But now try to use an icecube. Rub it gently along the foot. Always move the icecube and don´t keep it to long on one spot. The anemone should loosen from the rock. It was working here in South Africa many times. Never tried it myself, but it makes sense to me. If you go into icecold water, the softest body part shrinks first, hey?:lolspin::lolspin: