Huge misconception about pigs. Pigs are very clean and if given a choice will never go to the bathroom anywhere close to where they sleep or eat.

Pigs use mud to avoid sunburn.

« Some people have gone so far, especially with show pigs, as to slather sun screen onto their pigs when they know that they will be out in the sun for a considerable time and they don't want them to get dirty with mud. » -- http://petcaretips.net/pigs-sunburn.html

You could also just keep your pet pig indoors all the time.