The door to the run can be a weak spot, but there are ways to deal with that. I build a four sided wood door frame for the run door to fit closely into, with the frame on the inside so pushing on the door gets nowhere. This means I have to step up as I enter the run, but that's not a real problem. The apron that goes around the whole perimeter of the run goes in front of the door, too. Then I have two latches to the door, top and bottom.