You might try making silhouette decoys out of roofing tar paper. They work well for field shooting, obviously not so great in the water...
No need to paint or add colour for ducks, just leave'em black. Staple two pieces together to get a little thicker if you like (I do) and you can staple on a stake on if you want. I don't use stakes with mine. I just set them up in the stubble.
I've had excellent results in grain fields using about 40 of these silhouettes and a 1/2 doz store bought full body decoys. I'm experimenting on making some goose decoys the same way. BTW, any decoys work waaaaay better if you use a call. Duck calls and instructional CD are a great investment and with very little effort/practise can double or triple the effectiveness of your decoy spread.