i think gore brought up a good point though... one of the most important parts of physical security is to be prepared for social engineers. there are a million tricks that i have used for one thing or another (not just computer related) you never know who you can trust, so it's best to train your people to know what to keep an eye out for, as well as keeping open lines of communication. make people suspicious of people they don't know... it's better to be safe then sorry