To those of you using a topical such as Frontline with poor results:
Are you bathing your dog right before you apply it to the neck? Perhaps this is the problem! That medication adheres to the oil in the pets skin gland at the base of each hair folicle. When you wash your pet with shampoo, you are striping the oils from the skin. So the medication cannot adhere and ends up evaporating.
So after a bath, consider waiting 3 days before applying Frontline (or other topical flea medication). The only exception is if you are using a "soap-free" or "soapless" shampoo. Some brands that come to mind are Hylyt, BioGroom Natural Oatmeal, and I think Nova Pearls has a variety too.
Also, there are online companies selling knock-off Frontline or expired Frontline for cheap and they just don't seem to work at all. Consider your source.