It IS a good idea to rattle the feed can and call them when you go feed. That way if they do get out, they might listen to you and come back. I use a feed bin, so I just refill it when needed, but I do talk to them, maybe they would listen, maybe not.
Come heeeerrrreeeee leetle piggies!
Come baaaack to your pen so I can EAT you!!
We saw a clump of wild piglets in a pasture and backed up to get a better look. When we stopped, they spooked and instead of running straight across the road for the woods, they ran away from us, just over a slight terrace, which hid them from our view, then across the road and into the woods. I marveled that they knew to "hide" on the other side of that slight rise in elevation. Pigs are smart. In that litter of piglets were a few with distinctive Hampshire markings. Somebody's 4-H or FFA project got loose and is contributing better genetics to the local wild crowd!
My pig pen is fenced within a pasture fence. So even if they get out for any reason, there is still another fence to hold them. Since they would have a couple of acres to rummage through, I wouldn't expect any problem rounding them back up. My husband wanted me to attach onto the garden fence and onto pasture #2 fence. Nope. Don't even think about attaching to the outside parameter fence. LOL
Right now I have a 500 pound boar in it and he has made no move to root out.