Just to echo and expand Mike's point, deploying a shotgun (even if loaded with "non"- or less-lethal loads) is going to set you up for a pile of trouble, including (on the criminal side) ADW and/or brandishing charges and (on the civil side) any number of potential claims for physical and/or emotional injuries. You will spend a fortune on lawyers, then pay off the trespasser for a long time if you miss, or forever if you don't.
Generally,
- use of force must be proporionate to the threat
- displaying a gun or knife is using deadly force
- paying perps and/or attorneys really stinks, so you should go a long way to avoid putting yourself in situations where these might become necessary (in short, suck it up and move on)
Obviously, rocksalt isn't likely to kill anyone, so the consequences would probably be less disasterous for the armed citizen, but would probably be very ugly and expensive regardless.
Please don't think I'm jumping on your case; for all I know, you're talking about the racoons that are knocking over your trashcans at night.
By the way, the farmer across the street from where I grew up used rice, not salt. <g>