in (one's) back pocket
Available to be utilized if and when it is required, as of a secret plan, idea, or advantage. Keep that recording of your boss in your back pocket—you'll need it later if he denies what he said. The defense attorney has kept this eye-witness in her back pocket, just waiting for the right time. She has all the details of their unscrupulous business practices in her back pocket if they ever try to fire her.
Farlex Dictionary of Idioms. © 2024 Farlex, Inc, all rights reserved.