Hi Ron,
I don't think you're missing the gold, your later assumption is more likely correct. The sea tends to sort the lights and heavies, and often these are then buried, so even though you found the trash at 12 inches, the coins and rings will be deeper still, or more likely closer to the water in another place. Either an isolated patch, or in a long narrow line running parallel to the water, it could be just below high water mark, mid way between high and low water, or right on the wet line (where the angle of beach quickly flatens)
The moon, wind and currents all have a part to play in where the heavies drop out. When I start finding the light stuff I quickly move on scanning for the heavies. There are always exceptions of course, and I've found gold all on it's own with no particular reason to explain why it was in that position (not recent drops of course)
As Frank has said, every beach is a little different in where it habitually deposits the goodies. When you start finding lead sinkers, coins, and bullets, then slow down and listen hard because gold could be close <img src="/metal/html/tongue.gif" border=0 width=15 height=15 alt=":b">
Cheers
Kev