Squinky did say, initially that her set up was such as to make separation difficult. I, too have that problem as having no mains electricity on our land we can't put up fences with enough oomph to deter pigs.
I have overcome this problem by trading the use of a loose box, just across the pig's field for a bit of grazing for ponies when needed. I just trundle the sow over when her time comes and they settle in no time, making their nest and getting on with things.
Not everyone though has that chance.
What about a fence around the ark with fencing rail around the bottom and barbed wire attached to this?
Yes, I have learned from experience that you need to set your place up before you even think of breeding. Someone once said (Confusious, I wouldn't be surprised
) "Only a fool learns from his own mistakes a wise man learns from the mistakes of others" So, feel free to learn from mine!