I advise you seek the services of a professional sys admin to secure systems.
I don't think I've ever met a professional sysadmin who could defeat the evil maid attack. All the ones I've met would refuse to think about an attack vector if it implied they could not boot their servers.
Any sysadmin that claims to be able to protect against a physical access attack or its contextual equivalent is either lying or incompetent. In neither case should that sysadmin be considered "professional".
The evil maid attack would be useful against the system admin's workstation. Securing NOCs is beyond the scope of this discussion, but it is not difficult.