Lowie,
Yes can be frustrating, my advice would be to beg, borrow, steal a few of the millions of shotgun pellets laying around our country side and bury it, then using your coil practice pinpointing it.
Swing over the area until you get a signal, now step back and come in low and slow until you once again get a signal. Draw a line in the sand where you got the signal.
NOW, step around 90 and approach low and slow, when you get the signal again draw a line in the sand.
Where the two lines cross your target will be below.
Naturally once you get used to this method there will be no further need to scratch the lines in the sand.