Lesjcbs: No one can accuse you of not doing your homework. And not rising-to-the-occasion of answering tough questions. And yours is a breath of fresh air for also posting results on "finds" forums. Albeit humble, yet .... at least posted along side conventional metal detector show & tell finds. That answered my challenge of "if it works so good, why don't see their show & tell, like md'rs routinely do?"
I see you even did your homework on my "more plausible challenge". By comparing odds at one park versus another. To be fair, we'd have to also include the "total park space" per capita (because Central park is not the ONLY park in our town. There are dozens of others). So the fact of higher population here, is simply off-set by more (other) parks.
But even assuming we boiled it down to reflect exact demographics of age-of-park, population vs square footage of park, and so forth : I have a feeling that the same results would occur: That similar results could be obtained without any rods at all. Also , to be double blind, we'd have to also include the "dry runs" you might have had. What I mean is: You say you did try picking a spot at random (no rods) and found it to be sterile. But to be fair, you'd have to include if you ever also got the rods to cross, and found nothing.
Or to be honest and say that ...if the rods crossed, you're subconsciously going to "be looking 2x as hard" to find ANYTHING. Versus a blind stab spot you might be lack-luster in your effort. That sort of "bias" is where double-blind 3rd parties come into play , and various safeguards have to be in place. If I were in your state, I'd love to see if there's any increase in odds, versus landing on a spot (chosen by randomly throwing a tennis ball into the air) and finding it to be sterile.
But I do credit you with answering my question that you HAVE tried to see if your own methods have "more plausible" explanations. Thanx for getting back to us.