have a lock on
have a lock on (someone or something)
To have complete control over someone or something, or exclusive access to acquire something. Greg may think he has a lock on the promotion, but I'm determined to prove him wrong.
have a lock onhave an unbreakable hold or total control over. North American informal
Lock is here used in the sense of a hold in wrestling that prevents an opponent from moving a limb.
1974 Paul Erdman Silver Bears He would sooner see the whole bank go down the drain…than get beaten by us. Unless we develop an even better lock on him—and that won't be easy.