A trick I use for field hunting when the ducks are decoy shy is to take three decoys two hens and a drake.
Place the two hens rather close together ,about two or three feet apart. Place the drake decoy about seven or eight yards downwind of the hens. Hide yourself upwind of the hens and in good gunrange . Single drakes will usually fall for this setup and attempt to land close to the two hens. It's unlikely that a big bunch of ducks will pay much attention, but singles and small groups will come in close for a look-see. You know the rest.