What is a good word or two that means "The last person you can call on?"
For example, you've tried calling your normal plumber, but he can't do the job (primary), you've called your backup. They can't do the job. Now you're calling your ______ plumber, because they always pick up and they can handle anything.
I've thought of "end of the line" and "final" but they don't capture the idea of "the one you can definitely count on, but you don't call on them unless it's dire."
I've thought of "primary, secondary, tertiary" and "Primary, penultimate, ultimate."
But those don't quite capture the idea either.
Do you have a better idea?