The cap with a wife and key holder teaming up is outstanding. The thought of a slave getting so thoroughly double-dominated fascinates me.I deal with some of these same themes in my two latest stories on fictionmania.tv, CHASTITY TRAPPED and ON-LINE SESSION SCENE.
There's always some plot difficulties in keyholder-plus-other scenarios ... in order to keep the focus, I find you need more exposition. That's because the 'two keyholders' thing doesn't really work: having two keyholders makes it easier to get out of chastity not harder!
Or perhaps the two keyholders would support and encourage each other to NOT unlock him.
There's also an idea like a lockbox with his key in it ... and two or more girls have individual padlocks for the lockbox. But it can be hard to get that into a caption because I like my work to be entirely expositionary: there is no narrator, and no 'stage directions', just the words the woman says. And for her to get that lockbox concept in requires her practically lecturing the guy, which can easily sound so unrealistic it breaks the mood.
Maybe it would work as a series of four photos. You've done some nice work with the format in the past.