driveway issues....

I have a neighbor next to my business that has been very amicable for the last 3 years(that's when I moved in). Well he recently listed the property for $3.4MIL, and has since gotten rather touchy about property boundaries. Basically, since we moved in, we were under the impression that the back driveway that we all share was on an easement. That wasn't true.

So he listed the property, then all of a sudden he's out taking pictures of truck drivers in the driveway and telling them they're breaking the law. I went over to talk to the guy; he calls himself "Doctor." Doctor wouldn't see me, and sent a nurse out to do his bidding. I assured the lady we were very sorry for everything, and that we would try to keep these drivers off of their property. At the end of the conversation I specifically stated that our truck drivers need to drive through there, but we'll have them stop parking in the driveway. she said that was ok, since we had been doing it for years. All seemed ok, and I left feeling like any drama had been averted.

Well over the last week, we have stayed off his property, and told all drivers from other companies to do the same. 100% off his property. I mean, we never would have been on it in the first place if he hadn't been cool with it.

Today he erected "Not Trespassing" signs, and we received a letter from a lawyer informing us that we would be prosecuted if we trespassed again. So all that "good neighbor, ra ra" bullshit was just that.... bullshit.

I'm having our landlord, our lawyer, and our landlord's lawyer look into it, and I'm pretty sure we know what direction we are going to go in, so this isn't a request for any legal advice or anything. this is a post asking for any and all advice or ideas in regards to how I can fuck with this jerk. He's making it quite hard for us to conduct business, and all in an effort to sell his building. We're really good neighbors, and even had all of them over for a BBQ when we first moved in. All it would have taken is a simple conversation. buuuuut here we are.

So anyways, any ideas for how to be a really bad neighbor, maybe even make it harder to sell a property? All legal ideas please....

TL;DR - the neighbor next door to my business has closed off a driveway we have used for years because he's selling the building for 3.4MIL and doesnt want anyone using it. The problem is, he was a douche about it. so how do i mess with him legally, and possibly lower property value(i.e. junky yard, parked cars on the street...etc.)