My cheap 10 pack of decoys (from Bass Pro) has done well for 4-5 years now. One of them did get the head chewed up by a snapper, I assume, but still managed to stay afloat. I tie two decoys to each of my diffusers...one tied to the rope and another tethered to the first with a stout piece of steel rod (about 1/10" diameter). This rod keeps them from tangling together. Should one go down, the second acts as a backup. They do twist the rope, but that has not posed a problem in my pond. The pond gets less than normal wind action and only varies about 10 inches in water depth throughout the year. Keep in mind that I am marking my diffusers which get pulled most years for cleaning and rope inspection.

A true buoy would be best, but I'm too cheap for that (​lol) and the granddaughter likes the looks of the ducks.

Fish on!,
Noel