Not to drive it simple answer

Wash it weekly and dont let salt build up on it, i always used to give my run around a quick rinse no wax no proper wash, in theory it dilutes dirt and salt off the paintwork.

Actually by leaving your car really dirty puts up a thin layer of protection against salt and muck.

My run around died last week and it was £500 to fix it so i got myself a company car dirty diesel.