Other ways to id nails would be how the target's pinpoint. Sometimes where you getting the high tone in discrimate mode will not pinpoint right on. Also, especially with the etrac, coin hits will sound "clean and pure" with little variation in tone, iron falses will be pitchy.
Also, try circling the target when you get a iffy hit. Often times you will get the solid null when you hit the target from different direction, and you probably have a nail. When you keep getting the high tones from different directions, even if they still sound odd, you probably should take a look and get your probe closer to the target to see. And sometimes, you get over the target just right and you will get a solid hit if you get over the target just right......and it will be a good target hiding close to the iron. The etrac is as good as any machine hunting masked targets!!
If your new with the etrac or explorer, for a while you should concentrate on digging stable 2-way repeatable deep hits by sound/tone first, then by the TID #s second. And with confidence and experience you will then be able to decide the more iffy digs. And eventually you will be able to ID the iffy good hits from the falsing. Listen just for high tones with the etrac or explorer is not how it works, or everytime the target ID bounces into the coin range............you will drive yourself nuts.
When your hunting parks, let's face it.......there aren't going to be many easies left! And the locations in the parks where the deep iron lives, is probably #1 the oldest ground and #2 where some old targets are still hiding.
Brad