I just completed an International Police Mountain Bike Association course and they teach the "ABC Quick Check" - A for Air, B for Brakes and cables, C for Crank arms, Quick for Quick releases and Check for Check derailleurs.
As a self-sufficient home mechanic all my life I've never had cranks come loose but now that I'm working security I've found that, for some reason, it is a common problem on "police" bikes. 3 of the bikes where I work had wobbly crank arms when I started.