., that's a bigger problem, but some people charge by the square foot.

There's no charge but I can't just go posting links.

I've met other investors and contractors in the area, so I know how much investors are paying and what contractors are charging. 

A toilet can be $ 100 and a handyman shouldn't charge more than $ 100 for install.

Consider how many people you are willing to have before charging for extra people.

So if you lived there for 3 years, they shouldn’t charge you.

You definitely don't want a situation where someone gets hurt by traps or poison that you place.If it is more related to the tenants being pigs than a hole on the outside then it may require some education on how to keep things clean and charging them for pest control if local law allows it etc.

So my question is how can I protect myself if I do take charge of the apartment in the back.

I actually have no way of knowing for sure if he has gotten any of my communication, so there really couldn't be any kind of harassment charge.

Charge more for the rent back and have escrow withhold some money as @Andrew Boettcher suggested.