I live on a farm and have lots of tick problems. The Preventic collar is 100% effective. I used to get them from my vet, but Jeffers is less expensive.
I started using Preventic collars many years ago. They are the best thing that you can get to keep ticks off your dog. They also keep the fleas off. My dogs go all summer and do not have tick or flea problems. I highly recommend them. I always buy fro Jeffers because that have the best prices around.