Nice test.
My hubby will tell you that it will penetrate skin at shorter ranges and have to be picked out… and that it hurts. Yep, he was some place he shouldn’t have been 
no, actually he was taking a shortcut. Through a junkyard. Looong after dark. Didn’t think the fences were relevant.
The rock salt was though.
I would not recommend rocksalt for a home defense weapon. It will not stop a determined attacker.
I choose buckshot to defend my family with a home defense shotgun.
I also believe that using handloaded rock salt shells can give the prosecution some reason to cast doubt on your case.
If I pick up a gun, I want it to be loaded with the ammo that will do the most stopping with the fewest shots.
For me rock salt doesn’t fit into that picture. If it’s something that serious enough for me or mine to grab a shotgun, it’s serious enough for buck shot (pheasants, rabbits, quail, trap clays being the exception).
If it’s something that can be addressed with rock salt, then I’ll use OC spray or some other non-lethal.
I don’t ever want to think when I pick up that tool “oh it just has rock salt in it, it’ll be ok to pepper that individual” and then forget that had it still loaded from my last hunt or trap shoot and end up using deadly force unintentionally.
Hell yeah!! Looks like a whole lotta freedom right there!! 
Using RS in self defense is likely to land you in prison so I would avoid it.
“Why did you choose rock salt_?” “I only wanted to hurt them sir.”
“Then you must not have truly been in fear for your life… .”
If I have to aim a weapon, I am trying to stop a threat. I’m not trying to annoy someone. Rock salt is going to sting and be difficult to deal with, but it ain’t deadly.
I may have known someone, who during the hot summer days of their youth might have wandered into a nearby watermelon field to liberate 
from the tyranny of those who would not show the proper respect for a good watermelon on a hot summers day. 
Then would head down to the local swimming hole. 
That same someone may have taken a round or 12 of rock salt. 
They may have even left $5 nailed to fence, each time they came for a watermelon cause getting the watermelon without the rock salt was half the fun. 
But I know that was a looooong time ago. 
Semi-related subject. My wife needed a few shotgun shell casings for a craft project. It is for an upcoming wedding. The casings will hold small flowers that the groomsmen will wear. But she needed them to be orange.
The only orange 12 gauge shells I could find were less-lethal, rubber buckshot rounds. I must admit I did not know that existed. They are also marketed for animal control, etc. I remember thinking that it would be a good alternative to rock salt, lol. They would penetrate a cardboard box at 15 yards but would not come out the other side of it.
It would be no fun to be shot in the butt with one, just like the old rock salt.
Maybe add some pepper and other spices for small game marinating. 