
I don't use Frontline at all - the spot ons bother my allergies, and for the past 20 odd years we have used Program tablets once a month (or supposed to be once a month). They sterilise the flea so once it bites it can't reproduce. I think in the last 10 years I've seen 3 fleas total.
Because we use this I'm even more secure if/when we have pups because if the odd flea did get on them it's most likely bit an adult first.
Like I said I've not seen many fleas at all.
I do have Frontline spray (must check date) for the odd time we get a tick, but even then we've been very lucky and not had many.