For guys there is also the possibility to tie a rope behind the ball-sac (make sure circulation stays good, or even better, use a chastity tube!) attach a thin, nearly invisible string (fishing line works well) to it, pull it through his fly he is most effectivily leashed. The girl can simply knot the string to her belt and he has no choice that to follow her on the whole shopping trip - meanwhile being constantly teased and excited...There is a small chance it will be noticed, but that's really a slim chance.