Put up those fake cameras on each corner of the house place a post and a sign reading smile you are on camera One in the front yard One in the back facing the neighbor 

Type of tenants, driveway, hours, trash, cameras, fines, termination, crime as a reason for termination, etc. 

Fencing, cameras, lights of course if it is a bad neighborhood you could find things stolen. 

Hosts should be looking towards automation for safety reasons (like keyless keypad locks that the hosts change the code to each turnover and outside security cameras) as mentioned above.  

Borrow one of those plumbing cameras that can look inside, if it's money like in the movie Triple Frontier, cut me in. lol

I've heard of some landlords installing security cameras, but I'm not sure how scalable that is with multiple properties.   

Are you using a security system, cameras or anything else? 

Is it legal to install camera in the basement ?

We don't winterize, that's when I do any maintenance it needs or we spend a night etc....I have cameras, temperature notifications, leak detectors that will automatically shut the main off etc....and the mini splits are back up heat.  

Alternatively, my go to home inspector uses a FLIR thermal camera on every inspection and can tell a lot about what’s happening in the walls.