My vet recommended these collars after I told them how bad the ticks had been summer of 2012. I had to pull them out of 3 of my 4 dogs ears which was VERY painful. Since I've started using these there have been no more ticks in the ears. They do need to touch the skin which is a little harder for my dogs with the coats they have, but seem to work very well. The only complaint I have is it says they will drop off after 48 hours if they attach. I was still pulling ticks off their backs, BUT they were dead and drying up so the collars were doing their job.
Ww have a dog rescue organization. Dogs come in with LOTS of ticks. We do use Frontline on the smaller dogs BUT for the big dogs the best value are Jeffers' Preventic Collars, which work for several months.