There was nothing much available back then with a covered trigger.
We just learned not to pull the trigger until the gun was on target..
Most holsters wouldn't let a revolver cylinder rotate while the gun was in it.
By the time you cleared leather, it was time to be shooting.
I spent an afternoon shooting with Bill Jordan. He was so fast that he was starting the double action trigger pull when the gun cleared the holster, by the split second later when the gun came level the hammer was falling.
I did one heck of a lot of practicing, drew and dry fired every day before going on duty for 13 years. I never came close to being as quick as Bill.
As far as keeping the gun in the holster, many had a security strap. When you thought things were questionable, you could unsnap the strap or it would swivel out of the way. Officers learned to stand in a manner to protect their gun when in a "discussion" with someone.
That was a time when nobody even thought of screwing with a LEO. If a BG din't intend to kill him right off the bat, it was "Yes Sir, No Sir!"
If Bg intended to kill the officer, there wasn't any formalities, it was Oh S**t, and shoot time. The less you had to think about the better your chances of beating him to the draw.
Things get "purty quick" when you're watching a feller's gun coming to bear on your chest and trying to shoot before he does.