I would be taking them to task for putting THEIR fence on MY property, though. That's just plain ballsy and rude.
My brother (who was living with us at the time) called and said, "Um.. your neighbors are putting a fence up on your land." When we got home from work, hubby walked over and asked about it. Neighbor assured him that it was indeed his land. He was nice about it.. not rude and seemed to know what he was talking about. Hubby didn't really know for sure where the boundary was... though he thought there was a stake by the tallest pine that marked our property line. Since he wasn't sure, and the stake was gone, he didn't push the issue.
Neighbor stated that if we wanted to re-plant the trees we thought were on our side of the property line, we were welcome to do so, but otherwise we could just leave them on his land. We left them.
Nothing but a few posts were up for about a year, and then one day we came home to find more posts up and wire strung. I kept looking at that fence and thinking, "Gosh, that just seems awfully close... It just doesn't seem like that would be the boundary line."
We don't really use the land for anything, though our other neighbor (the farmer) makes the hay for us. Since there is now only a very narrow strip in between our dog fence and their horse fence, he won't be able to get in that area with his tractor which means either tall grass or us mowing it on a regular basis.
Fast forward a few weeks, after the fence went up on the other side of the neighbors property. Another neighbor, (We'll call him Neighbor 2 and the horse guy Neighbor 1) the one who sold hubby the land, happened to be outside one day when hubby was working in the yard and came over to chat. He asked if we realized that Neighbor 1 had his fence on our land. We told him we thought it was our land, but had questioned it and the guy acted like he knew exactly where the boundary was.
Neighbor 2 said that there used to be a stake marking the property (right by the pine where hubby thought he remembered it being). So, the trees we thought we'd planted just on our side of the boundary line are indeed very near the boundary line, and on our property.
Neighbor 2 also told us that Farmer Neighbor is extremely POed because the field on other side fenced in almost his entire parcel of land and was going to refuse to sell the people hay due to the fact that they'd stolen his land.
Shortly thereafter, someone had the land surveyed, stakes with orange flags were put up, the horses were moved onto the small field that is encroaching on our land, and the big field that is encroaching on Farmer Neighbor's land stands empty.
The kicker is this: shortly after throwing up the fence, Neighbor 1 was shipped overseas for the military so his wife and children are alone. THAT is why we're not pushing the issue with the land boundary. Before he was shipped out, Neighbor 1 told hubby he was eventually going to put up a more permanent fence and when that happens, you can bet that fence is going to go where it belongs.
If we decide we want to set up our property for horses of our own, their fence will have to move sooner. Until then, it's really not hurting anything and I do enjoy looking out the window and seeing the horses...
I really hope it was an honest mistake, though. It'll be interesting to see what happens with the Farmer Neighbor's side.