You are right, the ants definitely come back every year. Even if you tackle the ants successfully this year, using a common ant killer preparation, living conditions in your garden are clearly good enough for them to quickly re-establish themselves. A young ant queen will swarm out every June and September to find herself a stomping ground.
Since the often-quoted baking powder tip is most definitely an old wives' tale, the best long-term measures to take against the creepy-crawlies are construction measures. For example, lay slabs in gravel or mortar rather than sand.
Regarding the lawn itself, ants particularly like warm, bare patches with a sandy floor. That makes them more common on sports fields and playgrounds than closely-matted decorative lawns. So: Aim for as dense a lawn as possible, through seed choice, fertilization and care (including lime!), and the ants will have a harder time in your garden.