As an former pest control owner I would say that the best solution i know of is a product made by Advantis, Thermador At least i think this is the correct spelling.
It is undetectable by termites and the termites actually spread it like the flu to each other thru feeding.
A great backup is to also use Tim-Bor a salt type solution that is sprayed directly on the exposed wood surfaces under the house.
I also have used this for pretreating and it works great.
Tim-Bor is also used for the treatment and prevention of mold.