Say the Word - S3-E5
Visible crew/equipment: Governor is 'interrogating' Michonne privately about staying at Woodbury to "join his forces." As he mentions Merle's name, she suddenly reacts, grabbing her sword from him, and shoves it at his throat, threateningly. During this, the shadow from the boom mic is visible just above his head. (00:13:50)
Answer: The walkers could have knocked them down more than once. There may have been another wave that knocked down the fence earlier and they're going to put it up again soon.
Captain Defenestrator