D. Access control vestibules: Access control vestibules are enclosed areas or chambers at the entrance of a building that require individuals to pass through multiple access points. This can include authentication, such as card readers or biometric scanners, before gaining access to the secured area. Vestibules help in preventing unauthorized individuals from directly entering the facility.

E. Fencing: Fencing is a physical barrier that can be an effective deterrent and obstacle for intruders. High-quality fencing, especially if it's difficult to climb or breach, can help secure the perimeter of a facility.

Options A, B, C, and F also contribute to physical security but might not be as directly effective in stopping intruders: