I have 300-350 chickens on about 2 acres. I fence mine to the max (6 foot high welded wire with 3 strands of electric fence on the outside). I'm not worried about them getting out, its the stray dogs that we occasionally have come through. A couple years ago (before I set up my fence) we had about 200 chickens (19 week old pullets) killed by a stray dog. Came home to find feathers everywhere and the dog back there chewing on one. That by far is the worst chicken predator we have out here. It was devastating to say the least, so many dead chickens we had to get out the backhoe to bury them all. I also divide those two acres in three sections to let the grass recover. Besides that its nice not having to watch out for chicken poop all over the yard..