Essentially, the neighboring unit was recently renovated and rented, and there's now (and has been) water leaking onto the concrete slab, and through the bottom plate of the wall, and into our unit a little bit. 

We live in a small town and are looking at purchasing our first rental property in a neighboring town with population 7K.

My neighbors keep an eye on the house for me and I have heard no qualms.

He is kinda like squatter at my house now and causing trouble with neighbors. 

I guess with Condos, if the HOA is any good, at least you don't have to worry about common areas but then you have to worry about neighbors, bylaws, CC&R's, HOA dues, litigation, etc.

Another idea is to buy a portion of the neighboring lot (if that's possible) to add enough acres to your lot to add more units.

@Greg H. yes she is making big fuzz saying since fence is broken (it actually bend little) the neighbors dog can come and bite me, burner is not working cannot cook infact 3 of them are working and window not working properly so if there is fire i cannot escape and so forth

You could also try knocking on the neighbor's doors to see if they know the owner's contact info.

Still a great way to learn and its more fulfilling to drive by your retirement vs. watching the stock market. 

I hope they succeed and fulfill their note obligation.Any suggestion on how to structure this lending in our best interest?