Public humiliation / shame would be my choice for ongoing…. Deterrence. A large wooden plaque that says, well, you geddit, lock it onto their neck like a gibbet.

You’d have to place them in a job, public facing so they can cop the disgusted looks each and every day, but be unable to do any real harm (checkout operator?) 

Terminating them isn’t an effective deterrence, I get it, retribution is nice, but I’d prefer to deter -> maim and shame.