Jess,
Nope, I never dig a hole on an active sportsfield..(OldLonghair tried to tell you) . its just not cricket! Anybody, and I mean ANYBODY that sees you digging a hole there will bust a spring and you will get in trouble! You are hunting a junior high school/ sportsfield right? That means if you are looking for silver or gold rings, you should try to think about where the spectators sit or where the snow is pushed over by where the teachers park and along the entrances where the snow is shoveled, (generally based upon the predominant downwind) etc..(again, like what OL said) .Junior high kids will lose a little silver jewelry, but not many of them are wearing gold..their Mothers do though, so you gotta think about that and hunt the locations where the Moms travel...since you are hunting the Mothers for gold, you need to focus on foil signals, since most womens gold rings are little 2-4 grammers that tone in the foil...
I am not experienced at all with Minelabs, just hunting the kind of location you originally mentioned, generally for gold...so your brothers here will have to address that TID/tone issue...my first silver coin was also a merc, and it hooked me pretty bad too!

You WILL find lots of rings if you are just out hunting..more silver than gold ones, since its hard to miss that silver "ping" gold is tougher to find since the signals can be from high iron/low foil all the way up into the zinc tones! You got a top of the line machine, and you have access to some very knowledgeable brothers here on the Minelab forum, so you will be successful with it as long as you get out and hunt as much as you can and learn what it is trying to tell you...you get good and fast with a screwdriver (like tonopahkid told you) and you will get more targets in half the time than digging for them, which will shorten your learning curve immensely, put more targets in your pouch per outing, so then its just a matter of the odds in your favor..
I'm pretty sure you will find a ring along side the sidewalk where the main school entrance is...they are always there. Good Luck buddy, your Minelab brothers will help...read all the forums you can no matter what brand detector is being used, there are some pretty powerful hunters in this bunch.
Mud