I am in Texas and we have the same problem..only hardcore stuff works, it seems our fleas have gotten immune to some stuff.
We started Comfortis last spring and are very happy with it. So far no problems at all and I have three dogs using it, all various breeds all different ages. It haven't left a rash or any other negative reactio, the topical left two of my dogs (non B's) with a rash.
It seems a little high in cost but it works..so we like it.