Shallow targets are often the hardest targets to detect.

The number one question I am always asked is how do you detect deep gold? followed by what metal detector or search coil is the best for detecting deep gold?
In my opinion, far too many beach and water hunters are obsessed with trying to recover deep targets. 
A better obsession would be trying to recover easy to detect shallow targets. 
I recovered all of these gold chains and bracelets (Without pendants) on beaches in south Florida, not one piece of this gold was deeper than 6 inches. 

In fact, I often use the side of my foot to scrape away sand after hearing a gold tone on a beach because it is probably going to be shallow. 
I give myself every chance to detect shallow gold when using a VLF metal detector by covering the ground slowly and sweeping my search coil slowly. 
The slower you cover the ground, the slower you sweep your search coil, the more chance you have of detecting both shallow and deep targets. 
If you cannot detect shallow gold, you have not got a snowball in hells chance of detecting deep gold. 
So my answer to finding deep gold is to put all your efforts into finding shallow gold. Correct your beach or water hunting technique, as speed kills your chances of finding gold jewelry at the beach.
The gold chains in the photo do not look like they are worth much, but they are just appetizers for the main course of ladies rings with expensive stones. 
The majority of my best jewelry finds were all found within the first 6 inches of sand, the level of sand that most beach and water hunters struggle to master. 
Target recovery speed is greatly increased by being a slow poke at the beach, you can detect good non ferrous (iron) targets resting close to ferrous targets better when your search coil passes slowly over both targets. 
Even just a fleeting low or high tone can alert you to a good target being partially masked by a bad target. 
As crazy as it sounds, the way to find deep gold is to master finding harder to detect shallow gold.