Only Karyn and Jon can use the stone... and anyone they really, really like.

Jon said, "OK, that takes care of accidental loss. But it won't get the stone back to us if someone takes it. It won't stop someone else from making a harmful wish." Karyn thought of leaving a loophole in the wish they had discussed earlier. "What if we restrict wishes to just us, except for those we also approve of using it. And leave an opening for someone else if you die, no permission required. Then you can pass it on in your will like your grandfather did for you." "Sounds good." Jon considered the best way to phrase this. "I wish that, for as long as I'm alive, no one else except Karyn or me can use the stone, except if one of us explicitly gives them permission, AND that permission for others can be revoked by either of us at any time." Karyn approved of this addition. "Oooh, that's a good one. I like the revokable option, but we might not get the chance to take it back until it's already too late. We'll just have to be *really* careful about who we trust with it, but that almost went without saying before." Jon nodded. "If we trust the wrong person with it, we're still screwed. But I think we've got plenty of room for other wishes to control who can use it and how it's used."