i always seem to have 1 0r 2 out of 10 hens who will fly over the 4 foot fence.
But I usually let them out to free range every day. The LOVE it. The love to dust bathe in the sun, hunt for insects, and scratch around. They will scratch up your landscape, like flowers or vegetable garden. The LOVE the woods. lots of bug and cover.
I could not imagine NOT letting them out. I have lost one per year to hawks, but this was in their 50x50 foot pen. when they free range they have lots more cover and places to dive when overhead predators are around. In a fenced pen, they tend to run to a corner and thats where a hawk will get them. Id always recommend a ROUND pen.
I would not feel comfortable letting them free range on an open pasture. no place to dive for cover.
Of course at night they are locked up in a secure coop. It never fails, they get back in the coop and are on the roost by sundown. Many people recommend leaving young poults locked in the coop for a week or so until they are 'hefted' to their coop.