Greetings,
I'm in a rush to get a new fence in place to the sides of my backyard due to pending neighbors extensive landscape project. A year ago I had my property surveyed, the original rebar capped stakes were found. The property line running alongside the neighbor to the north is fine, straight shot and looks to be unobstructed by underground sprinkler system but is very close to 6 inches of neighbor's sprinkler distrubution box but I think all is well there - no known physical terrain issue with the north neighbor.
On the southside the terrain is more complex. The property line runs 3 feet behind a short rockery wall, ours is the lower level land, the property line is on the top edge of the rock wall plus about 3 feet behind the rock wall. Fortunately that should be ample space to place a fence and of course you would want the fence to be on the high side of a wall. Now a bit more complicated. The prior owner of our home placed trees approximately on the property line, so close that they will interfere with placement of the new fence. The trees were planted appox 10 years ago, fir type trees. Some of the tree trunks are just over the line to the neighbor and some of the trunks intersect or are over the line into my property. Approximately 6 trees in a line. The neighbor to the south is new and does not know the history of the tree plantings which were planted by the prior owner of our home. To the uninformed observer they otherwise look like the neighbor's trees despite our ownership of a few feet over the top of the rock wall.
I have a dilemma about the fence construction as it will be blocked by this row of trees bordering the south neighbor. I will ask the neighbor about his thoughts of the trees, does he care if we cut them down altogether, if not they are gone and no problem. If he protests I understand I can limb up the trees to place the fence in front of the trees (so long as I don't kill the trees) I will state that at least one tree trunk base is over the line to my property and I will plan to cut it down.
Am I ok in proceeding in this manner or do I give up some space of my property to clear the tree row entirely, fence inches over to my property but within minimum clearance of the rock wall? Moving the rock wall is not an option. Of course I don't want to give up any property and I'm concerned about necessary clearance to sink posts behind the rocks or otherwise make the rock wall unstable. It could be argued that the root ball of the fir trees is also pushing out the top row of rocks also making the wall unstable. Our prior homeowner who put these douglas firs in had no idea how giant these trees become in a generation and they grow like weeds where I live.
I find this a bit awkward situation and I'm fearful that there are special protections for trees which prevent me from doing anything to them when they straddle the property line. However, I have been told of a unique solution to band the trees with mounting posts that do not penetrate the bark and as the tree grows expansion slats are removed, but the tree becomes part of the fence.
Appreciate your advise.

