When the Dead Come Knocking - S3-E7
Continuity mistake: The first shot of Maggie waiting for the Governor to enter shows her wearing a black tank top with her shoulders bare. After he cuts the duct tape around her wrists, the camera pans up and she now has black bra straps showing on her shoulders. (00:26:10)
When the Dead Come Knocking - S3-E7
Continuity mistake: The Governor takes off his gun belt while interrogating Maggie, and a few shots later has it on again in the same scene.
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