The fences won't hold them. All farms have fences and ours does too. They will hold cattle for the most part, but now and again even they will bust a electric wire or feed where the grass is greener. The hogs can slip through water gaps, poor fences spots, and create holes of their own.

We have taken photos by a fence not realizing the backdrop, ... Oops. We have a small population of hogs that can be hunted that do not live in a lot nor get fed by us regularly . They are free to roam. We however do everything possible to shoot many and keep the herd down. We have more boars than sows, and right now, ... we kill young gilts on site. We want few sows to keep the breeding down.

They may very well explode in population ... ??? We hope not.

Hope that helps ...