i have 4 dogs and 3 currently have the Soresto collar.  2 of the dogs seem to be tick free, but still have fleas which have migrated to their rear end (the farthest point from the collar).  the 3rd dog has both fleas and an occasional tick., the last tick i found was up by the ears.  all 3 dogs were bathed and gone over to make sure there were no fleas or ticks on them prior to putting the collar on.  the 4th dog, (who is nursing puppies) currently has no type of medication or flea collar and ironically is flea and tick free.....