Ric -
The scope is really good for sizing. I don't know how anything could do a better job.
You send the probe down and contact the target. Bring it up and back down a 1/4" away and quickly build a cross pattern. I have traced shell casings, an 8" long radio antenna, and a piece of wire just for fun.
The gotcha here are coins on edge. You can't land the probe on them. You can't feel them.
On the otherhand, the 'scope punches through tinfoil. I have even punched through a piece of a beer can several times. You can feel pulltabs flex if the ground is right.
If you have a periscope, the tool to add to your arsensal is a hole hog. I can find and recover a 6" or 7" coin in less than 45 seconds. The hole hog, when guided by the periscope, becomes an amazingly efficient digging tool. Crap, you hardly even get your hands dirty! The traces of digging are almost nil and it is just incredibly cool to be able to see exactly how the coin was orientated in the soil.
So, the bottomline for me, is that I dig any and everything that the hole hog can get to. I do this because I want the target out of my way, as it could be masking something better. And I can do this because the amount of effort on a hole hog recovery is so marginal that it really isn't that much of a problem.
Oh yeah, if you fish, there is one MAJOR side benefit. If you stick the periscope in the ground, it will drive the worms to the surface!
Tim