Bit late, but... A lot of flavor oils sold out there are unsweetened though, and are essentially tasteless. I read somewhere that it's really the sweetener + fragrance that tricks us into thinking we're tasting a real flavor. So maybe without sweetener (stevia, agave, saccharin, etc) there won't be taste, so that might not encourage licking so much? There's so much fragrance in commercial products as is anyhow, like Laura said. Tea tree oils are toxic to cats though, and chocolate is supposedly bad for dogs (substitute with carob), so might want to stay away from those Lots of natural pet shampoo recipes recommend citronella, lavender, peppermint and pennyroyal (small amounts) though all eos can be toxic if ingested in large amounts. I don't think it should be that much of a problem if they're rinse-off, no? I'd worry more if it was a leave-on.