As often as you think you need. Dry firing is practice for sight picture, breathing and trigger control. Fun, but doesn't take the place of live fire with your carry ammo.
"...automobile, yard..." The what? snicker.
"...BUT, this means..." Most of that applies to the shooting games but not real life. Game playing drills are not training or practice for anything but the games. SD doesn't mean you're going into combat.
If you've allowed a BG to get close enough that 'retention' becomes an issue you're tactics didn't work. Ditto if you need to reload or need to move at all(you should be behind cover, not just concealment, from the get go). If you're shot or otherwise damaged(even not seriously) you will lose interest in anything else. 'Weak hand techniques' are the shooting games and movies/TV, not reality.
Mind you, adrenaline does a lot of things. Knew a guy who walked off the Dieppe beach with 8 bullet holes in him. One of which was a compound leg fracture, he didn't know about until the MO on the ship asked him how he got off the beach. But under most situations, when you get damaged, you stop. You do not change hands and keep going.