If you are a course designer for defensive or tactical matches, something I was taught, to set your watch alarm to go off at odd intervals, and when it went off just look around you and say " what if it happened here and now".
Here's a drill that so far I'm the only I know that has run, very simple, it's an exposure drill.
5 - 10 shoot targets, no shoots as you think, some pepper poppers.
Shooter is behind hard cover with rifle or pistol out and loaded, set the timer for 2 seconds par time, when the buzzer go's off the shooter has 2 seconds to engage as many targets as possible and get back behind cover, run the shooter again and again until all targets are addressed, but each run should be from a different position behind the cover, high. low, middle etc... I gave the shooter 1/2 second over the 2 seconds to respond to the buzzer with no penalty, every shot over 2.5 seconds, added 5 seconds. The cumulative time is used divided into the score.
The object of course is to not get used to exposing yourself to return fire, for very long at all.