When a new metal detector or search coil is released, the number one question asked is how deep is it?
Target depth is not the number one thing I look for in a metal detector or search coil, I am more concerned with detecting small size targets at shallow to average depths.
If you can detect small stuff at shallow to average depths you can certainly detect large stuff buried deeper.
The majority of my best finds were recovered from shallow to quite average depths, levels where target separation and my metal detectors sensitivity to small targets are always far more important than target depth.
You could say beach and shallow water hunting is simply about separating the good stuff from the trash, making sure you detect it so you have something good to recover.
Once you learn how iron and other non ferrous (Iron) objects help mask the stuff you are searching for at the beach, you will realize how target depth is ok but not the most important thing for a beach hunter.
Several times this year, I took deep seeking equipment into areas immediately after I recovered good stuff and recovered nothing more at deeper levels.
It was not there and that is often the case when beach hunting, not everything good or better is just out of normal detection range.
The old adage you have to dig through the trash to find the treasure is true, either dig the trash or find a way of searching over it to detect and hear the treasure you are looking for.
Separating targets is the real key to finding good stuff at trashy tourist type beach sites, in wide open areas with very little trash, use a slow pace and slow sweep speed to help you detect deep targets.
Ever notice how many stories of good beach or water hunting finds start with, I rechecked the hole and got another faint signal.
The same thing happened to me several years ago, when I pulled this three hundred year old Spanish silver religious artifact out of a hole I had just dug a small galleon spike from.