Finding it
We run the station and look for the place the soil lifts, the hiss, or the head that never gets water past a certain point. Then we shut that station off before the cut. Roots and shifted clay are the usual reason a fitting that held for years lets go.
After the coupling
The joint has to cure, then the station runs at normal pressure. We watch the repair and the next head. Call 346-642-6161 if you already dug and the water did not stop when the controller moved on. That may be the main, not the lateral.