I rub the dogs' coats down with diatomaceous earth; it's good for keeping all insects from calling them "home". I also mix a teaspoon in their food at one of the mealtimes three times per week. It takes care of internal stuff as well. Only bad thing about rubbing them down is: 1. it's messy, so it has to be done outside, and; 2. If their coat gets wet, you must reapply the DE after they dry because it washes off easily. It's also really good for their coats, skin, etc. because it's got a high percentage of silica. Other good thing is you're not stuffing your pet full of drugs just like doctors want to do to us!
You can usually find 10-lb bags on Amazon for $19-23 delivered and it will last a LONG, LONG time if you're just using it for pets. But it's also helpful to use a teaspoon a day for yourself also!