How to stop my boy from touching his private part now and then in the public... is not related to the urgency to go toilet... anybody can help?

how old is he? instead of telling my boy cannot touch, I set a limit told him he can only touch if he is in bathroom or bedroom....I read that we shouldnt make them ashame of their own body so far it works for him, maybe u want to try? for him definitely no itch or pain but simply because of the pleasure, sorry if tmi😛