In extreme conditions you simply have to stand an anchor watch.

We once anchored in the lee of Petit St. Vincent in a 2-knot NW current about 200 yards down-current of the reef. As we enjoyed the evening the tide began to switch and suddenly the though crossed my mind that if the current reversed it would pull our anchor out and it would probably not reset before we hit the reef. So we stood on deck with a beer in hand watching the tide from 9pm until almost midnight. Interestingly, the wind and tide balanced exactly and our boat rested contently about twenty feet directly above the anchor which we could see in the moonlight, the water being that clear. It soon became apparent that the tide would never in-fact completely flip and we retired for a good night sleep.