have (someone) on a string
To have great influence over someone. If you want to have someone on a string, flattery always helps.
have someone on a string
or 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.
have/keep somebody on a ˈstring
make somebody do what you want because you have control over them: Of course, he’s rich and powerful enough to keep several people on a string.This idiom refers to a puppet (= a model of a person or an animal) that is controlled with strings attached to parts of its body.