Excellent post! I wanted to throw in my 2 cents worth... Back when the Explorer first came out, I found a lot of targets in "hunted out" sites everywhere. Most of these sites were hunted well with many machines by many people, but they left behind the older and deeper targets that their machine or hunting ability were unable to detect. They also cleaned out a huge portion of the shallower, newer coins. These kinds of sites had a high ratio of old coins to new coins, but you certainly weren't digging them by the pocketful like the "old days"! I spent years taking "road trips" all over the Midwest to sites I had spent many, many hours online researching in advance for the best possible potential. Many of those sites were a bust - there wasn't much left to find. About every third or fourth site I visited did produce well... which is to say around 10-50 old coins. I remember places where every other coin dug was an old one, and some places I could have filled my pockets with hundreds of newer clad coins without a single older one.
I developed a style of kamikaze hunting on weekend road trips where I've always hunted fast and furious to cover as many sites as possible in a weekend, which meant digging only deep promising signals. In this manner I kind of got a sample of what each site had to offer and determined the promising ones to revisit on future trips to hunt them slower and more thoroughly. I rarely spent more than 15-30 minutes at any one site unless, I was finding several good targets. I chose sites that were small in size and in the thick of activity... city parks, church yards and public squares were my favorite target. These places saw very heavy use years ago and were small enough for me to do a fast scan in a short time. These sites are densly packed with targets and require little roaming between signals - almost like a seeded hunt. Large parks, fairgrounds, etc. took too much time to cover a lot of ground looking for the "hot spots", so I stayed away from them.
I found that some of these places, especially in the center of a busy city had seen little detecting activity since the "silver rush" of the 1980's. These sites had a lot of old targets deep and a lot of new targets shallow. there was a zone of around 3-5" deep where there wasn't many coins to be found and it made distinguishing deep targets all the more easier, so you could concentrate on digging a high ratio of older coins while leaving behind the shallow new stuff. This method will miss the odd old coin not deeply buried, but my goal was for a high success rate over the entire weekend of all the sites in the aggregate and not for each individual one.
The point here is that I met with very good success nearly every weekend I went out by adhering to my detecting methods above. I still had the occasional not-so-good weekend, but that will happen. I had my share of detractors and unbelievers when I posted my good weekends, but I didn't let it faze me... I posted what I found to inspire others to get out there and hunt for this stuff while it was still there to find; not for my own glory or ego. I also recorded info on every site I visited and how I did there.... valuable info that I have referred to many times to return to some of the better sites many times to continue finding good targets. I have come across only a few sites in 30 years of hunting that I would deem "virgin" sites. They were usually small churches from the 1950's to 1960's that gave up a couple dozen silver coins - quarters and halves included, but I dug a couple hundred wheaties and clad coins with them as well. An old hunting acquaintance of mine found a small 1910 church in the St. Louis suburbs back in 1993 that was a true virgin site - he dug well over 1,000 coins - 200 of them silver coins, in 3 weeks out of a yard barely 2 acres in size! What really hurt was the fact that I lived less than 2 miles from it! Goes to show that you don't have to travel far and wide to look for a good site, it could be right under your nose! There's got to be "virgin" sites out there, but it would take a large amount of luck and persistance to find one. Even if you did, you would be overwhelmed by all the clad coins and trash targets you'd be digging, or ignoring, to find the old stuff.
I still do the occasional road trip, but I have found that all my sites have been visited by other detectorists and I have to get really wiley and persistant to squeeze out more good targets. Where I used to set lofty goals of 30 silver coins and 30 indian pennies in one weekend back in the "heyday" of my road trips, I now set a goal for 5 of each in a weekend. Sure the finds have dramatically decreased over the years, but my passion for detecting hasn't waned a bit and I think that is what this is all about - not out-hunting someone else, but enjoying your hobby on your own terms and keeping that detecting spirit alive.
Take care and HH, Mike.