In their data centres, Google has traditional security methods like physical road barriers, perimeter fencing and security cameras and more advanced measures like iris scanners and file fragmentation and replication.
But by far my most favouritest part of the video ever was how they dispose of dead hard drives. They drive a piston straight through the disk and then send them through a crusher to blow them into smithereens for recycling. Check for it at the 3:45 mark. [YouTube via The Atlantic]