Empty Lot Question--Neighbor parking RV and mowing.

[Garen T.]

Hi everyone, I've been a member of this community for less than 1 day, but already learning so much. 

I own a duplex lot not far from where I live. It is postage stamp size and is the last of about 15 lots that now have townhouses. I've owned the property for about 3 years and plan to build this year.

I pay taxes and get it mowed once or twice a year, but other than that, I've been leaving it alone. 

Recently I stopped by and noticed 2 things. There was an RV parked there, and the field had been mowed. I knocked on the door of who I knew owned the RV and met a very nice lady who had started mowing the field, and stacking up rocks. We talked about the RV and she said it was a very temporary situation and would be moved back. 

I was out there a week later and found another neighbor spraying the dandelions so they wouldn't grow and go to weed. But, the trailer was still there, but there was evidence that she was mowing more.

So... what are my risks and options here? 

Let her keep parking her RV on my lot.

Don't mind that they seem to be maintaining my lot?

Put a fence around the property?

What do you all think?