Here at Timberland, critters that pester pups are a pretty much constant consideration. Frontline, as mentioned before, is the preferred first-line-of-defense hereabouts (to the tune of a whole buncha bucks ... we've got a whole buncha pups
). Having plenty of pups with which to experiment, and plenty of grassland, bog, and woods from which the pups can and do make ready selection of pesky pests, we've tried just about all the others, and have found Frontline works the best. In particular, it seems far less prone to washing off or becoming inneffective when the pups go swimming, which they do here all the time.
Once the critters are established within a dwelling or kennel, however you do have to take extra steps ... flea eggs can remain dormant for many seasons, maturing and hatching when conditions are right. You've gotta get 'em all the first time, and keep up the battle for a pretty fair time, or in no time, you'll be up to your itches in the pesky critters again and again and again. Try
Flea Stoppers borate treatment for carpets and furnture, including the pup's preferred bedding and lounging areas.
For particularly nasty infestations, immediate on-the-pet results are good with
Frontline Spray
There are lotsa other products out there, and, as mentioned, we've tried lotsa them. Your mileage may vary, but that's what's worked for us.