We use schedule 40 PVC pipe 12" diameter split length wise. They have a heck of a time turning them over too. Ours are ten feet long to accomodate several pigs at once.
Thank you ao much to all who posted answers. We have two pigs and were using a homemade wooden trough which my husband made. Being inexperienced, (although ambitious) it lasted less than one week. Thank you all again.
Wood will work, it's just that here in Florida they rot pretty quick. One little hint, if you want to make a wooden one. Screws, not nails. Also if you build a rectangular one, put a two by four across each end so they can't flip them over. That's what does the most damage, they flip them over and then walk on them. l=l. Something like that.