Frankilin,
Keep up the good work on both Roslin and Hunter's Hill. While it maybe Ho-Hum for some, it is very exciting for me.
I'm sure you are in for a long and sometimes frustrating journey.
I worked with a state archealogist in Illinois on an old ancestoral burying ground. The big advantage we had was, that the cemetery was on state park land. The Historical Society had published a book in 1970 that located the cemetery and listed a few graves. At that time some tombstones were on a nearby farm being used for stepping stones. When we visited the property owner, (this was before the State purchaced the land) he took us out to a hill overlooking a creek. It was a pasture we were sharing with his cattle. We only found one small footstone with two initials on it.
Long, long story. The park supt got the state archealogist involved and the county historical society and it all worked out beautifully. There were hickups along the way and it did take 3 or 4 years to complete the restoration.
I don't know anything about dectectors or dowsing but one of the gentlemen in the society went out and dowsed the area and put flags where he thought graves might exist. He probably had a hundred flags inserted. The state archealogist wasn't impressed.
The only thing I have ever used in trying to locate tombstones is a 3/8 inch diamerer rod about 40 inches long with a T handle welded on one end with the other end being sharpened modestly. Too sharp and when you continually strike rock it won't hold a point. The probing is basically nondestructive and you can almost outline the shape of a stone laying flat under the ground. The stones are typically 6 inches or less below the surface and flat. Of course the destructive part is when you want to dig something up.
I don't know whether the property owner would be OK with this type of operation but otherwise I suspect you may be in for a long wait!
Garry