Have you ever declared bankruptcy or gone into foreclosure?

Likely will have to go through the normal red tape and take them to court.

If he is serious, he can try to take you to court.

I’m not an attorney but I would think if this “new zoning” affects the resale value of your home (rental or otherwise) you have a pretty good case in court. 

Can you get a court order to sale (partition) if you cannot locate the heirs of an estate?

Do you have to declare your rental income?

My wife and I are the Declarant for 32 residential condo units that we built in Pennsylvania between 1984 - 1987.  

You might add the "shoe leather" avenues:- going to the county superior court and collecting:- divorces- evictions, get the landlord contact (plaintif)- delinquent real estate taxesDoor knocking FSBO signs, calling FSBOs in craigslist, using peoplesmart.com searches on owners of tall grass houses...

I believe there are a few states where there's a court case that says the MLS can't be Realtor exclusive (# 6 http://www.realtor.org/law-and-ethics/mls-access-litigation-summary), but in most states you need to have a license or be an assistant to an agent.  

If you are the type that gets a big tax refund back every year, change your declarations so you get a small (or no) refund, and more money back in your weekly/biweekly check.