Rust needs 3 things, air, water, and steel. When you add salt you increase the flow of electrons that increase the speed of the deterioration of the metal. So how do you prevent that. Wash the salt off regularly, dry the bottom of your car, because you cant remove air
, and then inspect monthly that none of your undercoating has been scratched off or chipped. As long as the under coating is intact and 99% of the time that's the issue. You wont have to worry about rust.