Currently my dogs do not have fleas. I treat them monthly year round, unlike some people who do this only durning the summer months. My sister has three dogs, who recently acquired fleas. First she tried Pet Armor, it worked for a few days, but the fleas returned and I suggested Frontline Plus, which I use, which only lasted slightly longer. Calling the vet she was told to treat her home as well as her pets, even though there was no evidence of fleas in her home, she did, it didn't help. Are fleas becoming resistant to certain products or are there other products she should try?