They have two gates—a front gate and a back gate.
That roof is just made for identification isn't it.
I think the "back gate" (as you called it) is more often used to send out the trucks that stock the "safe houses) than as a means of entry or exit for semi-undercover office workers.
The folks with exceedingly deep cover never visit the area, or are flown in from Eisenhower field at Fort Belvoir (20 miles or so to the South).