There is an ant poison called Amdro. It is small yellow granules, you sprinkle a spoonful near an ant hill, and they will take it into the nest. It takes a day or two, but it will wipe out the nest by killing the queen.
DO NOT put it where chickens can eat it! The only ants I've found that it is not effective on are leafcutter ants, they ignore it.
This is what we do too, Amdro works well on the big red ants we have. We put a board over the hill after treating it so the chickens can't get to it.
We've had tons of ants this year, our whole driveway had become an ant highway, so we had to do something.