I've carried .44 shot shells to deal with camp pests for years. Most people want to hear that bears or such are the biggest problem when backpacking, but I list 1: insects, especially mosquitoes, and 2: rodents. The rodents will chew through a tent to get at sweat in a sleeping bag. They can climb ANY tree to get at food hung there (a total waste of time, in my opinion, and not possible in most evergreen forests), and will chew through backpack straps, belts and shoes to get salt from sweat.
Shooting distance was never more than a few meters and the shot always killed them quickly.
I've never tried or even thought about rock salt. I never had to control big domestic animals. Just ran fast and climbed up tall things.