Keith wrote:
I've got an old stone & sand basement that has fleas really, really bad
from the previous owner (well, her cat). When I first moved in, a 10-second

ANY chance there are mice, rats, squirrels in voids around basement?
Possums, etc., nesting under a porch or in attic? If there are wild
critters bringing them in, it can be a risk of disease. Are you using a
"name brand" pest control company? If so, go up the ladder. They may
be using a product that doesn't kill eggs, and retreatment is needed
after a few days to get newly hatched fleas. Be sure no animals or
nests are present.