You used to be able to buy a decoy that was made out of 2-liter bottle. I used to have a dozen of them and eventually got rid of them. I don't hunt over bottles, but have down South where they used them as fillers. They had several hundred of them painted black and strung up with line attached to concrete weights. They made the weights by filling dixie cups with cement and adding a horse shoe shaped single strand electrical wire that was stuck into the cement. They seemed to work good as we shot lots of ducks over them.
I am a firm believer that duck decoys are sold to the hunter. I do prefer good goose decoys in high traffic areas as they get smart on decoys. Ducks get smart on blind or hide location along with no movement in the spread. For ducks movement in the spread and excellent hide are key.