Herbs for Flea Collars

I want to make a collar for my dog and I don't know what herbs to fill it with. What herbs repel fleas but still do not have a foul odor? I thank you for your help!

In her book, "The Complete Herbal Handbook for the Dog and Cat," Juliette de Bairacli Levy recommends flea collars made from woven eucalyptus. Levy advises other herbs – pennyroyal, fleabane (Erigeron spp.), and tansy – can be useful especially if they are impregnated with eucalyptus oil.
Whether or not any of these herbs are foul smelling is a matter of personal preference you will have to determine for yourself. Eucalyptus is a common ingredient in cough drops and cold rubs (e.g., Vick's Mentholyptus). Pennyroyal is similar to mint but somewhat more pungent, though not offensive to our noses. Fleabane and tansy are unlikely to offend in our opinion.