This is an unexpected programming application. It's nice that the farmer actually changed behavior after receiving the phone call.

At first, I thought there was a clear improvement. This problem essentially boils down to finding the intersection point of three circles. But it's also likely that with the small fuzz from imprecise time measurement that the three measured circles wouldn't actually intersect. I would guess that a small boost could be achieved by sampling points near the two intersection points of any two circles, but this is moot when it's just possible to brute force the whole grid.