To the OP, and I hate to say this, I am a land surveyor and I agree with so many others, make the guy move his fence over to the boudary line. I have done to many jobs where there are hard feelings between land owners and it can spiral out of control. I would have your surveyor talk to the guy and let he know this is the "offical line" and his fence is over it. If he doesn't move, move it for him.
I will tell a short story. I did a survey about 20 years ago. The adjoiner called and said our survey was wrong. We checked our work and it was correct and it turned out the guy had lost his ground because he wasn't able to keep up with the payments. In other words, sour grapes. Fast forward about 3 years ago people bought the adjoining land and we surveyed the land again and there was a fence on the new line and it was in the wrong place. I also found the markers from my previous survey, and at first I thought they were in the wrong place and I had made a mistake 20 years ago. After checking several things, I determined the guy had moved my markers 20 years ago when he complained and after I had left the job site and had then built the fence. When I confronted him, he blamed it on the guy that had built the fence for him. I talked to the new land owners about adverse possesion, getting a lawyer, and that I was 99% sure his adjoiner had moved the pins 20 years ago but I couldn't prove it. This new land owner did what I consider a pretty gutsy thing, he talked to the adjoiner about moving the fence but he wouldn't do it. He then went out with a bull dozer, took the old fence out, and built a new one on the correct line. He related to me he told the guy he would see him in court if need be. I always admired him for doing this, but he also knew I would go to court for him and swear the corner markers had been moved.
I can't recomend this kind of drastic action, but like I said, I admired the guy for doing it, and it turned out to the correct course of action for him to reclaim the land.