Not trying to be clever saying this
If a grave anyone is searching for shows no trace on the surface, then a spade is handy to take away part of the top surface and hopefully expose a stone.
On 2 occasions at City Road, i have exposed stones covered by grass etc for many years.

That thought would never have occurred to me. I am not sure I have the courage to do that!

Good evening John

Let me be clear
I am not suggesting you dig right down on a grave site
The couple of graves I found covered over in City Road were only just below the grass surface
Thinking about it, I probably used my hands to pull up some of the turf
A piece of metal rod to poke through the soil and hopefully hit some stone is another idea.

Give it a go !

Roger