The anemone should be anchoring itself if it is happy. But if it can't find a spot out of the flow it will not do well. When I had a condy I would basically sandwich (gently) it between several rocks out of the flow. It always seemed to work. I've always been under the impression that if an anemone is moving or floating around then it's either not happy or not healthy.
As far as the horseshoe I'm not sure. I had got a couple from Gerbers years ago and they were always swimming around. I have heard since that they have poor survival rates. Sorry not much help.