Are you asking for protection while working, or sport? Wild pigs are dangerous, fast, smart, hard to put down, and can get to 400-500 lbs easily and they may charge you, especially if you stumble across a sow with piglets. If the former I'd recommend at least a .41 mag revolver with BuffaloBore 265 gr. LWN or 230gr Keith bullets on your hip, or similar caliber semi-auto with one in the chamber ready to go. You may not have time to pick up a long gun.
If you plan on hunting them don't go alone. Find someone with experience, and use trained pig dogs.
Good luck and keep your head on a swivel.
PS: Here's some good advise from Chuck Hawks: http://www.chuckhawks.com/feral_hog_cartridges.htm