If your really sure you found everything...you probably havn't. I've been over certain areas till there was no good sounding targets left and eventually bought a new coil and then tested it out on these areas and found some good stuff, silver, buffalo's, ect. The funny thing is, most of those missed targets were not very deep. I always thought that all the targets left behind were just too deep to find, when in fact, they were just mixed with junk and the previous coils couldn't separate them. The new coil I used was the D2. It VDI's high on some stuff but I don't trust the screen anyways and dig everything above an established VDI for that area. At really junky parks I'll leave more targets in the ground. At old homesteads, I'll dig anything that suggests it is NOT iron.......+0 and above. The D2 can whisper sweet lies about bottle caps all she wants, I'm still digging the target either way. The fact that it gives a good signal on really difficult targets that would normally null next to iron, ect, is what I like about it.
The 12" coil is a huge concentric coil and I would expect nulling unless your already convinced the area is clean.
The 12" coil is a huge concentric coil and I would expect nulling unless your already convinced the area is clean.