Mythbusters showed that even welding a steel washer to the barrel of a 12Ga shotgun that the barrel wouldn't blow up. It sheared of the welds and blew off the washer.
For the rest, what are you guys doing, crawling through mud and sand for hours? Covering up the muzzle has never crossed my mind. If there was an instant where it touched the ground (3 times in my life, I'm 49 now) I'd just check the barrel and shake out what was in there IF there was something in there.
Keep the barrel pointed down, problem solved.
RC