We have a giant ant hill underneath the flagstone patio that surrounds a small koi pond. They have caused part of the patio to sink by their burrowing. How can we safely get rid of the ants?

Hi Debbie, The ants are probably enjoying the soft easy digging in sand around the flagstones. couple options: try flooding them out with a water hose; physically destroy the nest; or use pesticides such as permethrin or cyfluthrin. many ant sprays contain one of these products. Be sure to read and follow all label directions and keep product out of pond. If there is sand under the flagstone you may see nests periodically. Hope this helps, Sandy