Skyjac is correct in that one way to protect them is to keep them clean and waxed.
Another way is to clean them, degrease them, strip them of any contaminants and then clear them(spray them with clear paint)
There are also sprays that go on as a liquid and dry to a rubberized film. it can then be peeled off like a sheet of thin rubber(it's clear kinda)
Check it here:
Chemsearch