Can you use derbac on dogs?

You could, but there is no reason to. Derback is used to kill head lice, and there is no evidence that dogs can carry lice. If you intend to use it on fleas or ticks, well good luck. It likely won't work.

What will work is to rub your dog down with cut Oranges, lemons, limes, or grapefruit. It seems fleas and ticks hate citris, and citris is relatively benign for use on dogs. DO NOT use this home remedy on cats however.