This is a great way of looking at it. You take a broad look at it..
It's just that from an amateur standpoint, treasure hunting will become increasingly difficult with every silver coin plucked from the ground.. old school copper culture fragments that are worth money also become less and less as time passes. Not everybody has access to beach hunting 24/7.. and rings in parks is an oddity rather than a regularity. Even just clad coins will be mostly gone or covered in concrete jungle expansion.
One now passed on detectorist combed a village near. No , he didn't get it all , but he sure got some!
When the road was replaced he scored more.
Same village added sidewalks to the park. Which equaled not only fresh dirt , but depth of excavation.
That civil war era park has been pounded for decades. Yet still gives up an oldie now and then.
When those sidewalks went in the project (digging) gave me greater depth. And old silver.
The "bottom" of the park is rubble from a village fire.
Like other civilizations , there are layers of history. Some built atop others.
Whenever disturbed there is a chance of relics being exposed ,or in better reach.
Fill dirt....
Our dirt road had a lot of fill put on it. Stuff was imported with that dirt. From where?
Old payphone sites are invisible many places now. So too the pop/soda machines outside stops along roads at varied businesses. Heck , many buildings are gone and weeds and brush are all that is seen.
I know , cause they were from my youth.
Old buildings being razed sometimes hold secrets. As can the grounds around them.
Future detectorists may need not duplicate our common methods. But there are /were other methods being used all along that can evolve going forward.
Find the history.
Find where people gathered regular in small numbers. Or. gathered in great numbers briefly.
We have "brown" spaces in cities today. And beyond cities What was there?
What of towns bypassed by new highways?
What of the old railstops?
Coach trails?
Have they all been thoroughly searched?