I got rid of several thick invasive nests of ants on one small patio (not fire ants though) using two methods. It took two months.
First I sprinkled dry diatomaceous earth everywhere I saw them. Sometimes twice a day. It won’t appear to do anything at first. But they get it all over them and carry it back to the next where it is sharp and harmful to all the ants’ bodies.
The other thing I did was mix laundry borax into dabs of peanut butter, put them in old jar caps all over the patio where the ants were trailing. They loved it. Again, it is something they take home and feed the others and everyone slowly dies.
It took a LOT of work but this was after years (before we moved in) of the homeowners’ association spraying. The ant nests survived all that. But the spraying is toxic to all of us.