Really like where you are going w/ this....and liked the unique safety pin. Found one like it in Tecoma, and lost it there somehow.
I too wonder about the audio fatigue. I turn the iron audio down very low and give it a grunt tone on my machines, but its still annoying....and wish it was a more gentle tone. I keep thinking about nickels. I find lots of them, some even old and deep, here on my side of OR. But it took me til last year and several dozen ghost town outings to find my nickel out there. Why? OregonGregg makes a living on them in the ghost towns. I surmise it has to do w/ the nickels often blending in w/ the litany of low tones such that i sometimes get tone deaf and just don't react to them. Maybe they are getting pulled into the iron range where i tend to ignore unless very repeatable, or my gain is too high and I should shallow it up (i see Gregg getting solid VDIs from many nickel finds) to avoid pulling in deeper or surrounding tin/iron. Maybe they bounce across too many audio breaks due to the nearby particle of crud (need to check my breaks on my Ghost town programs) and don't sound good. Dunno. No trouble finding mid and higher tone targets. I do know that if I'm not digging nickels, I'm a lot less likely to dig a gold coin, as they often are going to come in on the lower end of the scale. Try the nail board test w/ a $2.5 gold coin. You will hit it consistently, but often it's down on the iron scale (-15/-20 VDI on whites), being pulled down by the nails. In some directions it hits around a 25. Thus, that coin will cover a VDI range of 40 units and depending upon audio breaks, it can sound like utter trash. Even if one were to only use 2 tone that some machines offer, it would still likely get passed over by most. Would be easy to hide that out there. I think you had a $1 gold coin...and I'll bet it gets pulled well into the iron numbers.
Anyway, I appreciate your thoughtfulness in regarding the how/why of your success. Great to see you get out and read a report.
Stay healthy!
Brian