I would never use rock salt in a shotgun. If you need to shoot someone, you need to stop them from killing you. Therefore, while I pray it will never happen, I will use real bullets if I ever find myself in that situation. If the situation is not so dire, you are not justified in even threatening someone with a gun, so rock salt is not much use. If you shoot someone with it anyway, you might get sued.
I doubt many people outside of police will have experience with stun guns or tasers. Personally, I carry a Kimber 1911 everywhere. At home it will either be that or a shotgun with 00 buck.
Again, though, I pray I will never have to use any weapon on another human being. If fortune is unkind to me and I become a statistic of one sort or another, though, I will be a mark in the 'successfully defended self' column.
Nick