Rust. Road Rot. Car Cancer. The scourge of the automobile owner. Nothing will kill a car faster than uncontained rust. Out here in the dry Southwest, rust is not much of a problem. Maybe if you live within a few miles of the ocean's salt air, a scratch or other unprotected surface may gather some rust after a couple years of exposure. But in humid regions, or worse, in regions of the country that put salt on the roads to improve traction during the snowy, icy winter, rust is a guaranteed occurrence.
There are those who subscribe to conspiracy theories who say that salt on the roads is part of a nefarious plot to insure that consumers will need to replace rusted-beyond-repair automobiles on a regular basis. And is it a coincidence that two of the largest industry's in Michigan is automobile manufacturing and... salt mining? I think not.
Combine that with the damage done to the roadway caused by salt runoff. Salt melts the ice and snow into water, the water seeps into cracks in the roadbed; the water then freezes, expands and creates potholes. The potholes need to be repaired by road construction crews and contractors whose jobs are dependent upon a steady supply of roads to fix. Do you think any of them are anxious to stop salting the roads?
What is the average automobile owner to do? Sadly, not much. Commercially available undercoating for the underside of your car and sealants for the painted finish can slow rust but never really stop it. I suppose you could hose the salt off of your car every time you drive, but that is not very practical. And many enthusiasts recognize the need to garage their collectible cars during times of salt.
But beyond moving to the dry Southwest or not driving your car during the winter, there is nothing practical that can be done from preventing the inevitable advance of rust on your car.