I also use live ducks - some are used as a sight chase and then some are used to help lay a scent trail to teach the dog to duck search on the water.
So I do like mustand does.........to stop a duck from diving - tape the wings - to stop if from swimming tape the legs but use masking tape as that will weaken with time in the water and the duck will get free if you do not get it back
We also teach duck search using a duck call.
We start young dogs by blowing the call and tossing the duck from a short distance on the water (your buddie tosses the duck)
You can add disance in time and even remove the sight of the thrown duck. The duck call is used at that point to get the dog in the right direction.
That is how we start our NAVHDA duck searches as we teach search.
JW