One sign of your dog aging which can be very upsetting if you don’t fully appreciate what is truly happening, is an increasing inattentiveness and apparent loss of obedience training.
When you call to him, your dog seems to be ignoring you, or else he responds so slowly that you tempted to punish him for disobedience. Nothing of the sort should be done!
Your older dog is, more likely than not, developing a gradual hearing loss. Both the loudness and the range of sounds are being reduced and account for what seems to be inattentiveness. These same changes, plus slight alterations in the nerve pathways leading to, through, and from the brain, account for his noticeably slower response once he does finally pay attention to you. To punish him, or to subject him to obedience retraining, would be a cruel thing which could easily break his spirit and build a wall of distrust and fear between the two of you.
It is quite easy to conduct an objective test of Duke’s hearing yourself. Be sure the room is quiet and there are no distracting sounds, lights, or physical vibrations. While he is resting quietly but awake, stand about five feet behind him, being sure he cannot see you. Loudly clap your hands together as you watch his head and ears. If his ears perk up and he turns to see where the sound is coming from, he can still hear quite well. If there is little or no response, there is hearing impairment to some degree. You should then try the same test a bit closer, again being sure that he neither sees you nor feels the vibrations or air currents created by the movement of your hands.
Assuming he does respond adequately, you may try again with not so loud a clap or by snapping your fingers, progressively decreasing the volume of the sounds. One caution; do not do these tests in rapid succession, as louder sounds may temporarily diminish response to succeeding quieter ones. Allow at least fifteen to thirty seconds to elapse between each decreased degree of sound. By means of such testing, you can establish the approximate level of your dog’s hearing ability as well as monitor it periodically to detect any further hearing deficiency. Keep in mind, however, that there can be a considerable variation in his ability to hear spoken sounds of differing pitch. Therefore his response may be quite different, depending on whether the speaker is a woman or man, child or adult.