You ever see on you tube where they use an ant hill for a casting mold for aluminum.

I notice in my yard if I kill off fire ants in a mound that a new colony would rebuild back in the same location.

My thought would be is to get a bag of portland cement which is not that expensive and take a bucket of water and gradually pour in the portland cement until you get a thin slurry mix that would pour into the ant mound chambers.

That would seal up the chambers when dry tighter than a gnats ass to a rain barrel.