A game of inches

The difference between going home with gold, or empty handed can sometimes be as simple as learning to control your search coil sweep. 
Every inch above the sand you sweep your search coil, is an inch less depth below the sand you are not detecting.
One way of maximizing the depth of your metal detector is to gently scuff your search coil across the sand.
Not only will you be getting good depth with a correctly set up metal detector, but you will also be sweeping your search coil level throughout the sweeping motion.
You are less likely to raise your search coil at the end of each sweep when scuffing your search coil across the sand, improving your chances of detecting deep targets all throughout the sweeping motion.
I go through many search coil covers every year, especially when I search over rocky or shelly areas on the lower beach or in the shallow water. 
My last search coil cover on my Excalibur lasted a grand total of three weeks!  
It can become expensive scuffing your search coil across the sand, but when you pull an expensive diamond ring up from the depths of Davy Jones locker the cost of buying coil covers in bulk is quickly forgotten.
I rabbit on about productive sites and beach hunting tactics, but my basic metal detecting technique is what puts those expensive diamond rings on my wife's fingers. 

Many beach and shallow water hunters use the same metal detectors for coin and jewelry hunting, your search coil control and sweeping motion may be the only advantage you really have over the competition. 
That is why it is so important to walk at a slow pace when beach or water hunting,  step, sweep and do not step forward again until you have swept your search coil in front of you from left to right and right to left.  
The next time you are on the beach, take the time to see how you cover the ground.  
Would your metal detector search coil be close enough to the sand to detect the heavy $4600.00 platinum and diamond ring in the middle of the photo before stepping forward? 
The diamond ring was really deep, it gave a feint low tone on the second sweep before stepping forward with my Minelab Excalibur. 
Exactly the same way I found a $6200.00 18K gents ring with a 5 carat emerald  back in 2012,  there is a lot to be said for sweeping low and very slow when covering ground with a metal detector. 
Sweep speed + search coil control =  depth and big gold!