ghost holes with F-75

I can easily hunt in heavy iron now with the 75, but had problems at a local park. First time using the unit looking for old silver. Had in de,4h,sens 99. I had 4 good repeatable high tones reading in high 80's that read from 8 to 12 inches deep. When started digging and got to about 6 inches deep stopped and ran coil over hole again and no signal. Since i didn't have my deeper digging equiptment with me I filled in hole and still no signal. No evidence of rust halo in the dirt I did get out. Went to another park in a different town i was in today and the same thing happened. I did get one nice signal at 7 inches high tone and VDI....rusted bottle cap. Does anyone know what i am experiencing?

get lost when opening the hole down to around 6" or so. My guess from experience is that another couple inches out of the bottom of the hole would have exposed the coin. Happens a lot to me with many machines. Many factors involved that Tom D could probably explain better. Using a pinpointer or checking the dirt pile in all metal for iron/foil is a good idea also to eliminate "foolers" and tiny shallow high conductors. Also, hot rocks will disappear like that but they generally do not sound off in pinpoint to begin with.

Tom

Would have dug further down, but since i didn't have drop cloth with me and was digging in rough area out from large old trees with roots to go through, I stopped as I didn't want to make a mess in the park. I will have to go back and dig on down in one hole in particular that sounded good but when I covered hole back up there was no signal of any kind. There was someone not far from me sitting in a car and i didn't want to look like some fool digging a basement just to find a coin, so I backed off.

Dig a small hole on the surface.... and a WIDE/DEEP hole underneath/underground.... and you will probably find that the coin kept falling deeper into the hole.... and ON EDGE!
If this fails..... Drop Disc to '0' and remove the mask that is in the excavated pile of dirt. It MOST PROBABLY will be a heavily oxidized/rusted bottle cap.
If this fails..... look for the blood spot (iron oxide) red/brownish discoloration in the soil ..... for the disintegrated Fe object. If found... keep in mind.... this may SILENT MASK your intended target. Spread the dirt and check again.

Tom