I've been using cattle ear tags cut in half and tied onto the dogs collar. They use same active ingredient [permethrin] as many of the "Frontline" type products" I've not found a flea on either my Jagd or Airedale. The tags are cheap and I change them monthly. They cost less then a dollar a tag so I'm looking at about $.75 for 2 dogs per month. I know I'm in the states but I'm sure you have similar products over there. Here's a link to what I use......
http://www.tractorsupply.com/livestock/livestock-fly-control/insecticide-ear-tags/y-tex-reg-gardstar-reg-plus-insecticide-ear-tags-pack-o
