What is the best way to get rid of fire ants?

the quickest kill will be a drench of the mound. Any of the water based insecticides that is approved for using around the plants the ants are near will work, even if you dilute the strength in half. Even on large lots that I treat this way with dozens of mounds the first treatment I would expect new mounds to show up three weeks later. After that treatment there should be some ant freedom for awhile though at any given time a new mound or two may show up but the yard is now manageable to treat as needed. Whether a new mound shows up 2 months down the road or two years will be impossible to say.