Trying Natural Flea Treatments. 1  1. Wash your dog. 2  2. Comb your dog with a special flea comb. 3  3. Repel fleas with lemon juice.  4. Treat your dog with apple cider 1  vinegar. 5. Try brewer's yeast.  6. Prepare a rosemary flea 1  dip. 7. Apply lavender essential  oil.