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. 

Can this prevent the starting over?

Then one day I had a scheduled showing w/ a potential tenant.Got to the rental, garage door wouldn't open.None of the lights would turn on.Flipped main breaker, nada.Everyone in the area had power but me.I had to show the unit w/ only natural light.The lady did not rent it, not sure if it was because of that, but the lack of power definitely didn't help.Turns out when previous tenant moved out, and asked power company to finalize his bill, it essentially shut off the electricity.I ended up having to set up landlord reversal w/ the utilities companies, to prevent the same thing from happening again.Lesson learned.

Otherwise time limits so far have been preventing us from doing it systematically .