Just wiggle it back and forth. With enough wiggling, it should come right out.
Good point BD. This past year I had all my ulities flagged, as its a free service,Just in case, make sure you know where your phone and gas or power lines are located if they are underground. And about a foot down and 18 to 24 inches above ground so the fence is not wobbly. After the first seciton you'll get the hang of it.