My thought about having separate lease agreements (Bedroom A, plus use of common areas, and Bedroom B, plus use of common areas) was to prevent my son from being liable for his housemate's rent.  

In came legislation and HOAs to issue fines and beat you senseless with rules to prevent any real profits.

@Wayne Brooks I'm likely going to have to go that route on closing day if neither have been done, but I'm just trying to find way to prevent that. 

Is there anything that I should be aware or take precautions to prevent these things from happening.

There is no way you can legally prevent investors from moving in on the list you provide them.

This will funnel into the shower base to prevent water from leaking down the walls and outside of your shower.

This has happened three other times.I have notified the tenants to make sure they don't just throw raw trash into the bins without bagging them up first, or to not throw in tall objects like a stick which prevents the lids from fully closing, then the odor draws the creepers to the bins. 

Even with a turnkey it will probably involve some basics like cutting grass, shoveling snow, maintaining landscaping, removing clogs in plumbing, fixing doors that stick or blinds that stop working.  

At this point he owes about $1500 in rent, possibly another $1000 for the cleaning charges after he clogged the toilet, plus any other heavy duty cleaning that's necessary after he vacates the property.He has refused to schedule a date to drop off the house keys but has said several times he will be out by 10/28.

Can this prevent the starting over?