I think one way to go is a reasonably high powered Pi used in conjunction with a descriminating probe.
Turn over the dug out sod - spread it out a bit. sweep with a small coplanar / DD - if Fe, tidy up and move on.
S
Turn over the dug out sod - spread it out a bit. sweep with a small coplanar / DD - if Fe, tidy up and move on.
S