Does he have contact with some other dog or maybe a cat. If he is mouthing of licking another pet that has fleas than he can ingest eggs with later become the tapeworm. Fleas eggs are laid in the fur of animals, in grass or in rugs, not in poop. They can only become a tape worm when actual egg is ingested, frontline takes 18 hours to kill an adult flea that has fed on the dog
You said you just moved there, did the previous owner have pets there may be eggs in the rugs, do you have an indoor cat or other small furry? Fleas can continue reproducing as long as they have a host to feed off of that has not be treated.