This is another of those ancient traps that I have known about for years, but never written on. Find a slope or hill near where the ducks and geese tend to be present. Dig into the side to create a tall-walled trench wide enough for you to walk in, but not wide enough for the birds to open their wings up far enough to flap/fly. Create a line of food, generally corn, leading into the back of the trench and then wait at a distance. Invariably the birds will find the food and follow it into the trench. Once they are far enough in not to see you coming up, walk to the trap and follow them in. Unable to fly, they are far easier to get your hands on. This is generally more helpful with wild ducks or unruly animals that are harder to catch than with domesticated ducks and geese that will just walk up to you if you have food.