Rather than your typical gates used by most villages, Sunagakure uses it's natural defenses to guard the city. A large crevice is the only path into the city from the outside, and it is guarded at all times by hundreds of men hidden in the rocks. Deep in the crevice there is a guard post with a normal set of gates, as it is still obvious that a check in point is needed.

Those wanting to access the city should check in with the guards before entering, or they will be tracked down by ANBU.