I have had GREAT success with DE! I live in the country, and during the warmer months the fleas REALLY come out! Plus there are alot of stray cats around, and all it takes is my brother walking his dog in my house, and all my ferrets get fleas super quick! It is usually hard to get rid of them because we have dogs, & ferrets, and the ferrets are usually hard to get rid of because they are always sleeping and have their warm spots!
So I usually rub the DE into the ferret hammocks, and rub some on the dogs... if it is real bad, I will rub some into the ferrets fur also! Just be sure to cover their faces because the DE just floats in the air like dust, and this will wreak havoc on any animals nasal passages!