Sorry for the delay. I was called away on an emergency. Thank you for all that great information.
The first thing that you really need to do is rule out hypothyroidism. Often dogs with hypothyroidism will have hair that tends to break off at the root during petting. It is prevalent in the breed and can cause aggression problems. You can read more about medical causes for aggression here:
If it is medical in nature, treating the underlying cause will help correct the aggression. However, it may also be behavioral especially if he hasn't had any real obedience training. The growling to indicate he doesn't want to do something does seem more dominance related. For that you will want to start obedience training. Even older dogs can benefit from formal obedience training though it does not have to be formal classes. The following site is helpful in helping owners train their dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
Be sure your wife also works with him on the obedience training. Use hot dog slivers. Dogs tend to like those as a treat and are willing to work for them. Each time a dog obeys a command even if for a treat it makes them a little more submissive. Once they see the owners as the boss, they won't growl to show they don't want to do something. In addition, they should look to the bosses (you and your wife) to determine if a person or dog is a threat and not act on their own to protect the property or themselves. Of course, YOU have to protect them and keep potential threats away as well.
Keep a leash attached to him and let him drag it. If he acts inappropriately, give a little tug to get his attention on you and a low toned firm NO to indicate that you find it unacceptable and won't allow it anymore.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.