You may also consider using hand signals with them early, so even if they do become hard of hearing, you can still communicate with them. (petsmagazine.com.sg)
Once the dog can look at the owner on cue, the dog can be taught to follow hand signals for all other basic obedience commands. (reference.com)
There are simply different ways to catch his attention and training will be done with hand signals as opposed to words. (petguide.com)