GolfTrap

Golf balls are denser than water.  They are also quite expensive.  Golf clubs (I understand) make a decent side income from the balls golfers lose in their course's water traps.

But that means that they have to extract them.  There are all sorts of expensive machines that attempt to fish the things off the bottom.  Alternatively, some clubs leave fine nets over the bottom of the traps.  This makes recovery simple, but it disrupts the underwater flora.

A better solution would, I think, be to make a duck-food dispenser.  This would be designed to give out a few duck pellets whenever a golf ball was dropped into it.  The birds would soon learn to retrieve the balls from the bottoms of the water traps in which they swim every day, and then to drop them in the dispenser to get their supper.

Of course they might also be tempted to steal balls from the fairways...