@Ronnie I think it was in the context of school playgrounds, specifically. Now that I think about it, I think it might have been implying more that it changes teacher behavior which in turn forces more artificial limits upon kids. When there's no fence, they keep everyone clustered close because it's easier to keep an eye on everyone whereas when there is a fence, they don't need to do that and since it's easier not to, they don't. End result is the kids actually have more freedom with a fence.