Eddie, I'm sure you know a thing or two about hogs by now, but just in case it's helpful: my opinion is that just about the only thing that'll contain a hog like Oscar is electric. If you only wanted to keep him in a small enclosure, you could do something strong enough that he couldn't get out, but for a field-sized area, electric is really the only option. Being as he's an adult, it'll be a little harder to train him to it, and if he takes a mind, he may end up just going through it no matter what, but it's your best bet.