For the last two years, I have been using a liquid product for horses, called in Canada UltraShield X, made by Absorbine, to protect my dogs from the pests that live in the bush. External products that are made for horses are good for dogs, and Aborbine now make the same UltraShield for pet protection.
It has proven to be very effective. It is a spray but but that wouldn’t work so well with a dog and I wouldn’t want to spray any in the face. I soak a sponge and rub each dog thoroughly through the hair, particularly around the face and ears. It lasts as much as a week, providing it doesn’t rain, and is more effective than the previous products I have used.
Absorbine is an US product and is called UltraShield in the US. www.absorbine.com