Find Short Circuits the Easy Way?

My circuit "toner" consists of an old RF generator tuned to an AM radio frequency and then adding a 400 hz tone to modulate the RF. Attach that to the circuit I want to trace, then I take a simple handheld AM transistor radio tuned to the aforementioned RF frequency and move it back and forth over the area where I "think" the circuit is buried (I use this on underground wiring & cables) and when I hear the 400 hz tone, I'm there. Just a little back and forth motion to find the strongest signal and then mark the ground in that spot.

Works every time, not fancy or expensive stuff. Just using tools I already have.