Shared Drives - Angry Neighbors

[Rick Turman]

So this is a pretty odd situation however it may have happened to someone else in the past.  I JUST filled a tenant in my Duplex and the very first night they stayed there, there was already an upset with the neighbor.  Bearer in mind we have a shared drive, this neighbor came knocking on my tenants door for them to move their cars so that she (the neighbor) could get out of the driveway since her daughter was parked behind her.  Once I heard this story I was like has this lady gone mad?  The drive is 16 feet wide, and fits two rows of cars.  Left is for our property, and right is for hers.  Turns our her daughter was in the shower too long and she had to get to a doctors appointment so she came and made my tenants move their cars so she could get out on our side.  

It get's better.  Lastnight my tenants reached back out to me stating 'It happened again!"  It was 8PM and the neighbor came out and saw my tenants parking their cars at the end of the road on their side of the drive.  The Neighbor asked if they could pull up all the way so that she can get out in the morning as her daughter gets home at 4:30 AM and will park behind her.  My tenants said i'm sorry this is a shared drive, and you have your half and this is ours.  Have your Daughter put her car in the street or simply have her move hers in the morning.  The Lady called my my tenants some vulgar names and bickered for a bit before going inside.  My tenants are getting heated and if I do not get this resolved, I may loose them and others that may move in.

I pulled my property line and deed and it looks like I actually own more of that drive then she, and that in fact my property line goes right down the half of this "Shared Drive" also shown on the sketch.  

What can I do or what has others done to mitigate this?  I can't kill the lady and we certainly cannot remove her from her house.  Those were ideas of the tenants which I thought was rather funny at the time.  I CAN however put a sign on the side of our duplex stating that This half of the drive is private property and any unregistered vehicle will be towed at the discretion of the owner to scare her off.  I could have a talk with her as I already relayed the message with her Grandson.  Can I put up a wall, chained fence, and or a few poles with horizontal cabling to show as a barrier?

I have provided the attached image for any suggestions as to how to approach this.  Thanks all!