I've used Dr. Bronner's peppermint soap. The stuff is powerful as heck and has a soapy aftertaste (it is soap after all) but it works great. The funny thing is that my kids use traditional kid soap and on a couple of occasions they've been caught saying dirty words so I wash their mouth out with Bronner's soap and a toothbrush. I use the same stuff for this "punishment" as I do when brushing my own teeth and they act like like was pouring ghost pepper juice in their mouth or something. I think that because of the situation, their mind is making the experience seem more intense and bad than it really is. It works though...not so many bad words these days.