Yes, a heavy mil clear plastic sheet looks just like open water on top of ice to beady eays from above ... at least until they realize it's too late!

I prefer using "bluing" that's used in washing clothes. I cut a small hole in the ice to get a 5 gal bucket into. Add a few drops of bluing to the pail and then pour it out on the ice and spread it with a push broom. Use as many bucketsfull as you need to get the hole the size you want it. Goes on pretty fast and covers well too.

With either the plastic or the bluing ... make an irregular shaped "hole in the ice" and set 5-6 dekes in the "hole and around the edges. You can hold them in position with snow or chips of ice. It's VERY effective if the ducks are looking hard for open water.