[SWHouston]

I use Trifexis and am ok with it, but, that's not all I do.

Spraying your yard is good, but you have to do it several times in close succession (about a week apart) to kill the Fleas.
Even with the above, they can still get some on them, and I am not beyond giving them a Flea Bath occasionally.

I think you just need to intensify your attack.

PS:
MlF is right, keep the dogs out of the sprayed area for at least a couple days.
You can always just do the back yard, and take them to the front to do their business on a leash.
Then switch.