Visible crew/equipment: You can see the casting directors on The Bridge behind Carol and Daryl wearing lime green vests. Then below The Bridge, you can see people driving their cars and a person walking in the parking lot. (00:26:57)
Visible crew/equipment: After Aaron refuses to provide his group's location, Rick tells everyone to eat and get some rest. When Michonne follows Rick outside it cuts to the car, and just as the camera pans to the right the actor's green nylon T-marker is visible on the ground, under the car door. (00:20:40)
Visible crew/equipment: When Sam comes to visit Carol with items in his hand, he walks through the front door of the house. Carol shuts the door after she lets him inside. As she does this, you can see the reflection of a black sheet or tarp of some kind covering the door area where the camera reflection would be.
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