When not at the OpenStack Summit, I had the (very) brief opportunity to play tourist and spent one day walking around the perimeter of the Tokyo Imperial Palace, home to the Emperor of Japan. The palace was built in the feudal era of Japan, complete with a moat, castle walls and reinforced large gates.
Today, there are guards at every gate, in addition to lights all around the perimeter and other surveillance mechanisms. There is even a no-fly zone rule, extending even to drones, that protects all the airspace above and around the Imperial Place.