PETER BLATCH says:
Most of the dogs I’ve seen upending for pricked ducks which dive to escape capture have come by it by accident.
All I can surmise is that while in pursuit of a duck the bird has dived in front of the dog and the dog has instinctively gone after it by pushing its head underwater – and been successful.
I cannot see the need to teach a dog to dive as most waters are too murky for it to see anything anyway.
The nearest I came to it was when I taught a pet dog of ours to pick a golf ball off the bottom of a tub filled full of water.
Early lessons consisted of just covering the ball with water but then, when the dog got the idea, the depth was very gradually increased.
In the end it would immerse its entire head to get to the ball but I stopped the ‘lesson’ at that.