Bug-biting-me, I am trying hard to sort through all the aspects of your quotes you give (from your permission seeking experience there), and wondering where to start. So forgive me if this runs long.
For starters, I believe you have run up against the following psychology: It works like this: Joe Blow walks in to city hall (or county hall, or the state capitol, or at the desk of a state archaeologist, or whatever/whoever public official you care to name), and asks a desk clerk: "Can I do such & such?" Now think of it: He'll either get one of 4 answers: 1) Sure, go ahead, have a ball. 2) Sure, but you must go through this many hoops to do so, 3) No you absolutely can not, or 4) why are you asking us? That's a silly question? You don't need permission to do that to begin with.
Now believe it or not, you will rarely ever get answer #4, even when it may well be the answer. Why? Because you are standing there in front of them, asking their permission, which implies permission was needed, to begin with (lest why would you go to them for permission, in the first place?). And with that inference in mind, you will easily get someone to say yes or no (usually the latter, as that's much easier for them). I mean, let's take for example, if I were to walk in to city hall somewhere and ask "can my buddy & I fly a frisbee in the park?" I bet I could find someone to tell me "sure, go ahead" or "yes, but you'll need to take out a group permit" or whatever. Using your own rationale, I suppose I could therefore deduce: "See?? The asking of permission was necessary, since ....... after all, they said 'yes' which means it was within their pervue of granting yes's or no's, otherwise they'd have laughed and said "why are you asking me?" You see? rarely would a desk clerk (or archie, or whatever) have laughed and said "you don't need to ask us". Which YOU take to mean, that therefore asking was necessary (since the mere fact that they gave you an answer, must, by definition, mean they have the authority to grant, or not grant you, the yes).
And as to the archaeologist's responses you cite, I fail to see where they quote any laws saying that no one can detect Georgia state land without their say-so. Except the disturbing of graves thing, which is the only actual law you/they cite. In fact, their whole answer is couched in "your inquiry and interest in Georgia archaeology". Huh? Since WHEN is someone's desire to go hunt coins underneath a bleachers, or around a concession stand, an "interest in archaeology"?? But guess what? Since you ask an archie, and since they, by their very nature, are usually anti-md'ing, they will GLADLY make that leap for you, and tell you that any such "disturbance" constitutes "archaeology". And PRESTO: "no you can't go". And you, the careful inquirer, are left to deduce "gee, it's a good thing I asked".
I can tell you of endless public places, on all different levels of govt, where no one cares, and detecting has simply gone on since the dawn of time. But if you looked long enough and hard enough (as you have apparently done), you can ALWAYS find someone up the chain of command and bureaucracy, to tell you no, on some level, with some remote connection of minutia. Yes, I gaurantee you that if anyone in the USA can tell you that they can just go to a beach, a sandbox, a park, etc.. in their area, w/o asking, and no one cares, it merely means they haven't asked far enough up the chain of command, to find someone to tell them "no". Or if they did get a "yes", it merely means they didn't ask high enough up, or ask with the right implications in mind. I mean someone can say we're doing archaeology if they want, someone can say we're "collecting" (which is usually forbidden at all levels, to keep people from pulling up in a pickup truck to help themselves to rocks, sand, turf, etc....), or they can say we might harm the wildlife with radio frequencies we emit, or they can say we'll damage or disturb things, etc.. etc... etc ... You can always find a way to get a "no", if you ask with the right preconceptions in mind, to the right personell. If you get a "yes", I gaurantee that if you keep going to different city dept's, or overstep them and go the county, then the state, and then the fed. level, you will eventually find something that restricts you to your own backyard (with your wife's permission, of course!).
Ok, disecting some more: Your contact cites no laws (except the graves disturbance thing), but does say "you'll need the permission of the landowner (which in this case, is the city level school district). To that I would say "yes and no". Because "yes, you have to have permission, so to speak". But that "permission", in the eyes of the law, can also be "implied consent" or "implied permission". In other words, just like the frisbee analogy, it is implied that you HAVE permission, if there is nothing specific that prohibits it, to begin with. Ie.: we taxpayers are ALREADY allowed in the park to recreate. Yet that permission can be "revoked", if a public personell uses his judgement to deduce that some nuisance is going on. Which is to say, that even though detecting might not be specifically dis-allowed, a public servant (cop, ranger, gardener, etc...) can still say "but I think you're harming the earthworms", etc... So as far as their saying "ask the landowner", is ....again .... couched in some sort of archie's preconceptions that what you are about to do, is somehow illegal, needs sanction, etc.... Ie.: that it's archaeology.
So please: get the law that these guys you quote, have in their mind, that says you need to go through all these hoops, to begin with. The only one they cite so far, is the graves thing. The rest is just their text, for this letter (ie.: "since you asked, here's what we say you must do" type of thing, with no laws to back up what they're saying). Once we have those laws they allude to, that say you can not disturb any public land, and any such disturbance is automatically "archaeology", then we can talk some more.
And if they can produce such a thing, it might be along the lines of a topic that came up about this, in Kentucky a few years ago. There too, some upper level archies were trying to say that no one, anywhere, could dig on any level of public land, within the state. But upon further scrutiny of the actual laws they were aluding to, it becomes obvious that the "sites" that are forbidden, are ..... archaeoligical sites! They jump from that, to a false premise that the entire state of Kentucky IS an archaeological site! But I clearly found elsewhere that sites have to be individually DECLARED as such (sort of like how England has what they call "scheduled" sites, for instance). Will that stop an archie in that state from saying otherwise? Probably not.
It would be like asking the PETA president "can I leave my bunny in a hot car for 30 minutes while I run into the store?" Well of COURSE they'd say "no", and threaten you with animal cruelty charges, etc... because they are fanatical animal/bunny advocates. And so too, are some "purist" archies so focused on hatred to anyone who dare digs a bottle or coin, that they too would easily tell you "no", even if it didn't actually hold water.
Trust me Bug-biting-me: detecting goes on a public schools, beaches, parks, etc... in Georgia, and no one goes and gets those archie's permission. And amazingly, they don't end up in jail, face fines, etc....
This is CLEARLY a case of "No one cares ...... UNTIL you ask". If you doubt this, search around amongst Georgia md'ing enthusiasts, and you will easily find people who hunt parks, forests, beaches, schools, etc... Ask them "did you get an archaeological permit?" and see what they say. At most, they might have asked the local school board (or more likely checked the wooden sign at the entrance to see if there were any prohibitions, and left it at that).
Here's threads on the whole psychology (the vicious circle) that you find yourself in now:
http://forum.treasurenet.com/index.php/topic,249049.0.html
http://forum.treasurenet.com/index.php/topic,164453.msg1198415.html#msg1198415
but in Georgia, State law dictates what we have to do to hunt on public land. 
The school grounds are deemed public land because it is owned by the county school board. The state also dictates that the State archaeologist be given five days notice before digging on public grounds, even when you have written permission. Believe me, I have researched the law 
and communicated with both the DNR and the school board. 
I know other states have different rules, but they don't apply in Georgia. 
In all my 35 yrs. of this, I have YET to have anyone standing over me with a calculator doing the math on the age of the coins I find.
