I've had Dcat2 at the vets for vaccination recently and they found fleas in her coat, even though I've been using the spot on treatment. I asked the vet about good alternatives to the spot on and she said the seresto collars were an option, has anyone used them and do they actually work? Both cats got a spot on treatment from the vet which is better than the over the counter stuff so they are covered for the next few weeks, but the collar is supposed to last a good few months.