There are a few other threads on here about this.
When Frontline did not seem to be effective I tried Advocate which cleared the fleas immediately. Last Winter when the dogs were getting wet every day and I could not guarantee they would not dilute the stuff before it had got into the pores, I used Nexgard tablets which are made by Merial, the Frontline company. I have seen no fleas and it has been very effective on ticks, the ticks do not seem to last long enough to engorge and every one that I have found has been small and dead. Unlike frontline when they were still wriggling and had filled up when I took them off. I am going to use Advocate for a few months in the summer because it is good for lung worm and the old dog has become a revolting slug hunter! Advocate is not designed for ticks so I will be observant and always carry an O'Tom tick twizzler.
Alan