Twice this morning I have read posts where people have asked this question.

How often do you go through your rentals? I have a friend who rents to college kids, and he "offers" to change the furnace filter every month for them. This allows him in the property and he can see firsthand what's going on.

He also mows the lawn every Saturday, which gives him more time with the property. 

Yes, this isn't scalable, and that's not what this question is about.

How often do you or your property management company inspect your properties? Do you write it into the lease that you will inspect this frequently? Do you schedule these inspections far in advance? Inquiring minds want to know!