Physical access means you're pwned. And it's not something nagios (or whatever you use) won't warn about since the server has to be briefly turned off and physically opened up. By the time you're unracking the server the police will be readying their handcuffs behind you.

All you have to do is breach the server room, open the server case, insert this raspberry pi memory module into the DIMM slot, and reboot the machine.

I have an even lower cost way of attacking the server. A simply cast iron axe could be used to smash the rack and access the motherboard, after which I would simply rip out the hardware.

Hold my beer while I go install webcams inside my colo servers!!! lol