Thank you for the encouragement and the education, I honestly hear ya, while the benefits would outweigh the work done, a signal yielding a depth of 8" is almost guaranteed to be a coin from the 30s/40s era at least, the very low sound wasn't encouraging enough especially when the location is not too secluded, the calculations in my head included those of 1) human proximity factor 🧑🤝🧑 as I am calling it along with 2) "what the heck

are you doing to the park with an 8" hole and similarly deep" factor and the 3) what-if just aluminum/bottle cap 🍬factor after all that work factor? If you multiply the 3 together, giving each factor my approximate weighting score, say, 30% x 50% x 10% , I got 1.5% encouragement to dig! ; ), I just got to find me more promising and secluded areas that do not have a lot of trash!! It just might be a tall order! The research involved appears daunting.
Digging deep in a urban setting.
1st: Cut a plug in the shape of a U.
Leaving a hinged side.(won't dry out)
Cut the plug with vertical sides (not like a saucer)
2nd: Pry the lid of the plug up. ( this should be the sod, with its roots)
3rd: Use the pinpointer/detector to see it the target is in the sod or deeper.
4th: If the target is still deeper loosen the soil up that is in the hole.
Note: Go from edge towards the center. (Less chance of hitting the target)
5th: Now push pinpointer in and around in the loose soil. If target is at the bottom still go to #6.
#6: Dig into the soil and press the soil into a ball. Repeat if necessary.
(Have a piece of cloth/plastic lid or what ever to place the ball(s) on.)
#7 Now dig deeper until you recover the target.
The original cut plug hasn't grown in area, only deeper.
Things to remember.
Dirt is 30% more in volume once its disturbed.
Now to fit the balls back into the plug hole.
1st one, press dirt, then follow with the others.
Leave the last dirt loose, flip lid closed.
Stomp heel down, fluff the grass back.
Smile at the good job done with zero impact showing on the grass.
I've dug in the urban grasses of the GTA and without a single complaint.
The staff of High Park always waved and never gave me grief.