One of the most common reasons pets get fleas is that they have dry, flaky skin, which makes it easier for the fleas to get a foothold and is easier for them to obtain their meal of blood. If the animal gets adequate exercise they will not have as many fleas.
I am as fussy about my animals as I would be about a child. No chemical please.
Sweet Smelling Flea Shampoo for Pets
1 cup Castile soap (liquid)
Place all the ingredients into a jar with a lid and shake to mix well. Add the mixture to your pet's bath water and the fleas will be very unhappy.
This is plenty for 2 small dogs or 1 large.