Older dog afraid of strangers

My Shepard mix is 11 years old. He has never been aggressive in the 7 years I have owned him but I have noticed in his older years he has gotten shy around strangers.
He will growl but never show his teeth, if your face get to close to his he will lunge and snap and yip as if he is being hurt. After doing this he always drops on his back or runs to his kennel and hides.
It is so hard to tell when he is going to do this, sometimes he seems fine with a person, letting them pet his back and even putting his head in their lap. These bursts of fear seem to come from nowhere.
He also has some strange fears, things that have bothered him since I got him. Fast movements, men with dark glasses or hats, new items in my home, long pole-like objects like brooms.
What could possibly be causing this erratic behavior and what can I do to correct it?

Then don't do it.

For behaviour change in an elderly dog, you should consult your vet. It could be pain or eyesight related, or even the first signs of cognitive disfunction. Your vet is the right person to advise you.