Probing for lost stones & parts is a slow tedious process that is unlikely to find the missing stone or part. I write this in an attempt to get more folks involved in finding lost stones, because the more we have looking the more stones that can be recovered.
I will use a common case to show the "how to" of the
procedure. It is for a husband who died unknown whose stone is missing, and
a wife b. 1804 d. 1850. The wife whose stone is still standing died in 1850
at age 46 and we are looking for the husbands stone which is buried next to
his wifes for one reason or another. Assuming her unknown husband lived
several more years he likely did not live long enough for the styles of
stone to change to the multi part monument. Therefore chances are he has the
same style stone, assuming he was given a tombstone and not just a
fieldstone. If his death was after about 1875 (in the south) the monument
could be one of those multi-part stack type. In that case at least some part
of the monument usually survives to tell us there was a grave stone there.
In that case and others we at least know what we are probing for.
As for those older long stones like a monument for our monument for the lost husband they have bases or bottoms that are buried sometimes up to three feet into the ground. Therefore the only way they fall is they are set too close to the (eastern) front of the softer grave soil and they topple in as the grave sinks. This is usually rare. In most cases the long type stone breaks off. With investigation the only way you would not know there was a stone there is that the breakage occurs at or below the ground level. The top part in that case has toppled into the grave sink and become covered in the sinking soil and debris. I find these sometimes and usually they are no more than 4 inches below the surface. If the grave is on a hill the top sometimes the fallen parts slide down the hill and may no longer be near the grave. That makes the stone or parts very hard to find especially if they are covered in debris.
When I get that familiar clink from the probe bumping the smooth stone at a consistent depth I dig them out and set them back up. In rare cases the fallen stone is deeper than 4 inches but in that case most times I miss them because I don't probe much deeper than about 4 inches. If the stone top is deeper than 4 inches it is probably lying in the grave sink and even worse is a stone covered up in a grave sink and a good Samaritan fills up the grave sink forever hiding most of the evidence of presence of the grave.
I must add here off subject it is good to get old
limestone monuments back up from the soil. Leaving them on the ground thus
keeping them damp can cause the stone to crumble in the long run and the
closer to the surface the fallen stone is located the more danger of
crumbling there is. This is because the stone is then subjected to extremes
in changing temperatures of the weather.
If the base is sticking out of the ground and next to a spouse's grave that is your clue that the rest of the stone of the lost spouse is nearby. However there are cases of the top of the stone missing because of vandals stealing it. Another unfortunate event occurs when the stone was soft (defective anyway) and the wet ground basically melted it away to never be found again. Many times the stone crumbled because there was a forest fire that burned it creating a softer stone that eventually begins to crumble away. Sometimes you can find the crumbly parts still present but that depends on the extent of the crumbling away. I am only referring to the old soft limestone or sandstone type tan or gray monuments, because modern granite monuments do not crumble though they can be broken by falling trees and vandals.
To make a grave probe get a 3 foot or more screw driver (found in specialty hardware stores) and sharpen the end with a grinder by slowly rotating the point against the side of a moving 3,000 RPM grinder. This makes the tool dangerously sharp on the end, so handle this with care, and of course use protective gear to make this tool. As you are building the point remove and dip into water occasionally to keep the point from getting too hot. Too much heat will otherwise make the point brittle.
Maybe with a
little luck someone will uncover a stone which has been missing for a lost
member of a heritage search group.