Great hunt Gary. Sorry you were feeling bad......... You did much better than I would have with food poisoning/stomach flu.
Keep using the horseshoe button. If you get a great signal that is fairly deep in the mid to high teens to up in the mid 30s that just hits in one swing direction and not the other or if it is repeatable on one axis and you turn 90 degrees and it is gone, the horseshoe button check is a good idea. Anytime I get a deep, somewhat iffy signal in the 20s and 30s (silver- PLEASE) I always check it with the horseshoe toggle. Sometimes US quarters and silver coins will be accompanied by a few iron responses if they are +8". If there are consistent, repeatable iron responses however and just one target (check with the pinpoint feature) it is usually iron of some kind. Also, larger than coin sized objects can be much deeper than the depth indicator. You can size your targets with the Nox in pinpoint mode pretty easily. Smaller coin sized targets will have small, well defined perimeters unless they are on the surface. Larger than coin sized objects will have a much bigger and less defined perimeter. Also, back in detect mode big deep targets will beep well above the ground surface while a small deep coin will stop beeping very quickly.
If you get under power lines, you can also do another noise cancel. It might help.
Good luck.
Jeff