Repellent #3. 1  Get the ingredients―1 cup vinegar and baby oil, 1 tablespoon dish soap and Skin so Soft, 1 cup water, and ¼ cup Pine-Sol. 2  Take all the ingredients and mix it in a bowl. 3  Shake the bottle properly before you spray it on the horses.  The spray will keep flies and gnats away, plus keep the coat shiny.