I now see more wisdom in such a “job protector”.
I feel a critical component could be
– the release process like the one your colleague controls
– build process
– some scheduling tool like autosys. You can make it very complicated.
– some home-made diagnostic tool to troubleshoot a critical component.
– some wrapper component that everyone must go through to access messaging, or some critical library…
– some very important SQL query? Well, colleagues can copy it and figure out how it works. It's “more effective” if there are many such queries and these queries need a lot of tweaking each time. Then no one can become familiar with these queries and replace me!