Neighbor problem over boundary line. Good fences make good neighbors?

I feel like I have been here before. Neighbor moved into house next door, but this is the country—we each have an acre. We are separated by a 10 foot deeded county path. However, he is acting like my line is his boundary, and is ignoring the county line and the ten feet. Wouldn’t be a problem except that he said I cut down a tree that was his, and it wasn’t. So, I don’t want to have a bad situation with this guy, even though he seems very aggressive (pulls out county markers indicating his own property line and put huge market on mine, for example).
Question is: what to do? Should I write him a letter saying I don’t want a problem with him (we don’t know each other), and explaining about the county line (can’t believe he doesn’t know it’s there…), or write the county and get permission to leave those markers in—and trim trees on county property—(of course it’s the Mt. Rainier and Puget Sound view), and copy him the permission letter, or offer to vacate the property, and we each take 5 feet (probably will increase our taxes). Just so annoying to have this stupid situation, and life is really too short. What I do know, sadly, is that if I ignore it, he will be able to claim the whole ten foot line—and it’s quite big. Advice?