I've been wondering if I should put my 11 week old puppy on flea preventatives. We live in San Francisco and we won't be going to any highly populated areas any time soon since he has not received all his shots. I've been looking up brands and K9 Advantix II seems like something I would be interested since it repels mosquitoes and I don't plan to put him on a heartworm preventative. I've heard a lot of horror stories about dogs developing neurological problems and other problems after using K9 Advantix. What should I do?