Never used the back entrance and never intend to, like others say it's easy to walk along the road keeping your head down and just turn left / right into the main front door which is open so no hanging around on the street.
I've been to a couple of places over the years and gone up a metal fire escape to gain access (including my 1st ever punt), not only does the fucking metal clang with every step but you are elevated up so everyone hearing the noise can turn around and see you as you ascend the stairway to heaven.