Factual error: In the opening scene and throughout, young Sam Anderson, cloistered in his bedroom, is presumably listening to a crackly 45 rpm copy of Nick Lucas crooning his 1929 hit, Tiptoe Through the Tulips. In reality, the disc with gold/blue label spinning on Sam's turntable is not the song playing. The original Tiptoe was released in 1929 on 78 rpm vinyl by Brunswick Records, and was finally pressed on vinyl 45 by Accent Records in 1974 (solid robin egg blue label however, not gold/blue).
Continuity mistake: The Wolf is shown to have filthy teeth but when Carol confronts Morgon in The Cell, his teeth are clean.
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