Judy,
I watched Ed's "Training Personal Protection Dogs" DVD a while back and came across something that might be of use to you.
Now this DVD seems to be an older one, so maybe Ed has changed his method since then, but he dealt with teaching food refusal to a dog.
The idea is that because we're asking the dog to do something unnatural and hard to understand at first (refusing yummy food), we keep the training very low-key and easy on the dog at first.
In the DVD, the handler is sitting on the ground relaxing with his dog and a stranger tosses food to the dog. The handler simply puts his hand on the dog's face and gently redirects his attention away from the food.
Every time the dog looks or sniffs at the food, the handler calmly and gently pushes the dog's face away from it (saying a quiet gentle "no") and focuses its attention back on himself.
The dog quickly learns what is expected, and the handler starts adding distance.
Eventually, when the dog knows the exercise (ignore the food), the handler can step up the corrections and goes further and further away from the dog, eventually leaving the training field.
Ed says to repeat this exercise under as many different situations as you can (including at home in the yard) until the dog is solid.
I'm guessing that taking food from a stranger and going up to stranger to get loved on would be discouraged the same way.
Could you try something like that on your walks?
Maybe have someone walk up to you and talk, with Gunnar by your side. If he tries to go up to the person or nuzzle them, just gently pull his face away from the person and back towards you, saying "no" or "nein" in a gentle tone. Keep repeating this until he gets it (praise every time he chooses to ignore the person on his own).
You can gradually increase the distraction level (someone he knows, in the yard, a group of kids) as well as the level of correction for "breaking".
Include the food refusal too - I personally don't want my dogs taking food off the ground or treats from people.
Not worried about poisoning but of them getting fed junk (you know, pet shop treats, yuck).
If you never want him to fuss over people (besides family) that could work. If you want it to be on a permission-only basis, then maybe use a command & a release so that you can tell him when it's ok to go get loved up
I realize that the food-refusal training may not be foolproof when the dog's on his own, but obviously in your case it's not like you're leaving Gunnar out in the yard for hours on end to fend for himself so I don't see why this wouldn't work.
If I were in your situation, I'd give that method a try. The training shown in the DVD was very easy on the dog - very little conflict. The whole thing was relaxed (with the handler sitting on the grass, petting and talking to his dog the whole time) and the dog quickly picked up the training.
Good luck!!
(PS: while my young male was always very aloof with strangers and never accepted treats from them, my female was impossible to train in terms of ignoring strangers. She's such a damn suck for attention -- you'd think we never pet her at home! After 10 years of this, I tried the above method on her and it was a very quick fix - without ever giving a single correction!
In her case, I only need her to behave in my presence, I don't leave her unattended in the yard anyway.
She seems fine BTW - I don't think I destroyed her spirit by doing this, hee hee
)