I think that the only way to truly prevent an accidental discharge is to not carry with one in the chamber.That having been said my surmise is that most of our pup owners keep one chambered when on duty.
When I examine the hammer,slide orientation on my R9 the hammer sits recessed into the slide.With a chambered round the back surface of the hammer does not protrude outside the slide.Since the slide can not be pushed any further forward once in battery the hammer is shielded from a rearward blow.
Jeff