Stilly's idea of using a the tone on a collar is a good one. One of my old dogs went deaf early and I taught her to Hup/Sit and face me with the vibration mode on a collar and from there she would take hand signals for retrieves.
It is suprising how much a dog uses their ears. Hunting with her in the brush after she went deaf was a challenge for awhile, she was forever getting lost. Slowly she learned to keep checking on me visually, whenever I'd see her start leaping in the air I'd wave my hat over my head and she'd head back in. We hunted together for 14 yrs, four of them with her deaf. She was one of the best, won a number of hunting competitions, first AWS to pass senior hunt test level in AKC spaniel hunt tests(too bad it was as a demonstration dog) and is the feature AWS in Barron's "The Sporting Spaniel Handbook". She was a hunting machine, her ashes are buried next to our favorite duck blind so she'll never miss a day in the marsh again.