PETER BLATCH says: This is a very common problem in gundogs, but to stop him using its eyes rather than nose, you should refrain from sending him for retrieves that can be seen!
Instead, plant hidden retrieves in longish grass or light cover and send him for these. To make things more interesting for the dog, cover the dummy with rabbit skins or pheasant wings held in place with rubber bands. The extra scent will ensure he uses his nose to proper effect.
To sharpen up the reaction to your whistle, try getting the dog out in front, hunting. Now blow the stop whistle and, at the same time, throw a dummy into the air to land in an area away from the dog.
Do not let the dog run in. Instead, hold it in the stop position while you walk out and pick up the retrieve. You will soon find that this simple little exercise not only gets his attention to the whistle, it also imparts much needed steadiness.