We managed picket fencing (had some spare) with boards across the bottom for ours as we weren't sure if we would only do it once and didn't want to pay the earth for something we weren't sure we would enjoy. They had a good go at digging underneath and tried pushing them over but it did the job until butcher time.
Seeing other people's setups we will do stock fencing next spring, looks really good and strong.
We did make a straw arc with a tarp roof - worked a treat and was so warm, cosy and dry in there despite the awful rain we had. We did make sure we built it on the highest point in our plot though so it didn't flood.
Good luck pigs are fantastic!