These products should not be mixed together. There is no valid reason to mix Onslaught and Permethrin SFR together. They are both synthetic pyrethroids so there would be nothing to gain by mixing these products together. Making a pesticide too strong can actually backfire. Areas that are treated with this overly concentrated spray will be repellent and insects will simply avoid the treated areas prolonging the infestation.
Yes, Permethrin SFR is labeled to be used directly on animals. Please check the label for specific instructions on how to apply to your dog. This product is not labeled for cats.
We do have ZoGuard Plus for Dogs that is labeled for fleas. Invert one tube over dog and use open end to part dog's hair. Squeeze tube firmly to apply all of the solution to the dog's skin as a spot on the dog's back between the shoulder blades. Use entire contents of tube vial on each dog. Do not use multiple tubes on one dog. Weigh your dog to be sure you are applying the right dose formulated for the weight of your dog. Separate the treated dog from all other dogs and cats for 24 hours after treatment has been applied.