I have been involved in searching for graves in marked cemeteries and
unmarked areas.  To me there is only one method that aboslutely guaranties
the location of graves:  grade-all the topsoil off.  This will work in any
situation where a grade-all can access the site, including areas of fill.
Probes provide too little information, especially where grave shaft fill is
comprised mostly of the soil the graves are dug into.  Radar and
magnetometer are subject to metal disturbance, salt infestation (from road
salting), non-grave variations in soil strata (roots & rocks), etc.  For the
time and money spent I find it best to jump the high-tech approach and go
back to looking for features with a shovel.