Preventative measures against rust?

I live in Minnesota, and it the winters the roads get salty. Pretty much every 92-95 civic i've seen (including mine) has a problem with rust that forms right above the bumper by the wheel well in the back of the car. Its basically the part where the metal meets the plastic.
The last owner of my car wasn't very caring and didn't wash it enough during the winter.

My main question is how to prevent this rust from forming, besides washing your car every couple days.
Thanks for any feedback.

The picture below shows the problem area: