Try switching to Frontline Plus this year. Sometimes, fleas can build up a resistance to one kind of drug. The Frontline may be more effective for you this year. Just make sure you use Frontline Plus - it's way more effective than the regular. :gj:
Oh, and it can take up to 3 months to get rid of them once they're there - even if its not a full blown infestation - so I really would start now. ;)