Like Brandon said your servers should be physically secure because if
they have access to your physical infrastructure is pretty much game over. Whats to stop them from just taking your hard drives?
If you want one extra layer of security, you can set a
password on your GRUB as well so before they can make changes to it they have
to know that password. But again, they
will have physical access to your infrastructure (or admin access on your
Virtualization platform) and either of those basically is game over from a