Smowball - I have exactly the same issue as you. My little girl's legs look awful and I now insist she wear socks to her knees in the house which is going down really well with this hot weather!
So far I've front lined them, but unfortunately allowed them back in the house straight away so I assume most of the fleas jumped off to join the other fleas hatching in the carpets. Last weekend I spent a bomb on flea powders for the house, and I've been hoovering hoovering hoovering ever since. Still got fleas. Now I've read the answers in this thread I'm not getting frontline again but will go for the other thing, and also I've got some killer flea spray on order from my vets coming on Saturday. I'll keep you posted!