This has little to nothing to do with the dogs prey drive or ability to hunt. This is all about willing acceptance to follow a command. Look at it in this way – the dog is reluctant to use its number one tool (mouth) on you’re terms. You’re best bet will be to take the dog thru a “force fetch” program.
Any trainer will offer a Trained Retrieve or force fetch program – $300 and up usually.
Force Fetch has a bad sounding name but it is not hard on the dog, you are simply making the dog respond in the correct manner, with no room for getting out of the command.
The most common method starts out with getting the dog up on a table and making it hold the trainers hand in its mouth without struggle. Then the dog is expected to hold – not crush or chew – an oak dowel, bumpers, retrieve dummies, coke cans, etc, etc, progressing all the way thru a live pigeon.
Once the mouth is willingly used on all items the command is brought off the table and onto the ground. The dog is given the command to pickup the bumper – again with no room for rejecting the command allowed – often called the force to pile. This is where you will 100% get over the duck issue, as a dead frozen duck is one item that can be used in the “pile” which is really a line of dummies laying close to each other.
Be wary of any quickie fixes offered to solve you’re problems here – giving in with the mouth 100% is really what you need. A quickie jam a dead duck in it’s mouth till it holds it routine will more than likely lead to a dog that spends a lot of time swimming around the boat playing confused.
Even if a dog has a great natural retrieve, there is value in doing this in that it trains the dog to follow commands which includes more than just the fetch command with willing acceptance.
Good luck!