The edge of detection range

I often talk about how the majority of my best beach and water hunting finds were recovered within the first six inches of sand, but I do detect and recover many cracking finds on the edge of detection range.
The edge of detection range varies with the type of metal detector and the size search coil being used, also the matrix the detected target has been detected in.
A slow methodical approach to beach hunting will help you to detect targets on the edge of your metal detector depth range, giving you a chance to actually hear an often "Iffy" target response at depth.
The slower you sweep your search coil the better a deep target on the edge of detection range will respond.
Keeping your search coil close to the sand will insure you have a chance of detecting "Deepies" in the first place. 
If you swing a 10 inch search coil four inches above the sand you will only detect targets six inches below the sand, every inch you swing your coil above the sand is one inch less you are able to detect metals below the deck.
Walking and sweeping slow and low along the beach is the only way to experience the thrill of pulling up valuable targets from the edge of detection range. 
If you search tourist beaches the big mamma jammer gold rings you are searching for are probably going to be recovered from deeper layers of sand. 
At shipwreck beaches old coins and artifacts are often way down in older layers of sand, shell or rocks.
These two old Spanish buckles from the 1700s were recovered two full moons apart using a pulse induction metal detector at a Treasure Coast beach, the signal responses from both artifacts were a break in my metal detector threshold. 
Check out the hand file marks on the one buckle and the pin still attached to the other, I love me some Spanish buckles!

A slight drop or break in a metal detector back ground noise can easily be a deep target, a slight tick of a signal from one direction can also be a deep target.
Whatever the deep target you are not going to hear it unless you are traveling across the beach slowly and sweeping your search coil low and slow.
Targets on the edge of detection range they are often difficult for a discriminating VLF metal detector to identify, the better the VLF metal detector the better the discrimination features.
Unfortunately most VLF metal detectors will classify a target on the edge of detection as junk, giving wonky FE/CO number readouts, bouncy target cursors or other incorrect VDI target IDs on popular VLF metal detectors. 
There are many things to learn about beach hunting, understanding how targets on the edge of detection range respond and what they could possibly be comes with experience.
The first step towards being able to detect high value "Deepies" is always getting to know your metal detector really well, using good search techniques and being able to identify easy to detect targets.
Once using your favorite metal detector and identifying targets within detection range becomes second nature, you'll be better prepared to understand the nuances of targets on the edge of detection range.