have someone on a string
have (someone) on a string
To have great influence over someone. If you want to have someone on a string, flattery always helps.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
have someone on a stringor
keep someone on a string
If someone has you on a string or keeps you on a string, they can make you do whatever they want, because they control you completely. It's so unfair — she keeps him on a string and he's crazy about her.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012