To keep the jail-breakers in. We originally did just a 5" fence around the run area, more to define the space as 'poop central' and keep the dog out. Of course, the birds eventually starting roosting on top of the fence. Then they just said 'what the heck...let's take a trip' - which would be fine with me, but my neighbors all have dogs (so do I), we don't have roo for protection, and blah blah blah they need to stay in their yard. So, this past weekend we added 3 feet of chicken wire to the top of the fence...so now it's like Alcatraz. Works great, but the ladies are NOT HAPPY WITH ME. They charge the door to the yard when I open it. They're hostile. They stare. With judgement in their eyes. I fear they are plotting some sort of coup.