Our ggg grandfather who was a deacon there must be rolling in his grave out there behind the church if he knows that so many of his descendants have done backslid on him!
Since you maintain a couple of cemeteries, what's the best way to repair a marble stone that has broken? I've seen everything from cement to bathtub caulk to roofing tar . . . .
If it's a really old, slender slab of marble I'd suggest either tile grout tinted to match or some variety of superglue/gorilla glue sealed with clear caulk after it dries. Caulk isn't too good long term if very much will be exposed to the elements as far as appearance, but it does keep those elements out of the crack, an important consideration if freezing is a concern.
Heavier stuff requires heavier stuff. I've seen cement. I've seen cast iron rods used sort of like dowels, an older professional repair I suspect.
So, the answer is “it depends,” lol. What you're able to work with for reliably adhering it into place, plus a sealant that sits well aesthetically, if your adhesive, cement or what have you isn't effectively sealing the repair in and of itself.
After replying I realized that it had never really dawned upon me, that there are a lot of ancestry groups and church committees charged with the same task,and that there would be a consensus of sorts reached over the past decade or two regarding how to go about this.
Here’s a very thorough PDF off of Ancestry.com:
http://www.rootsweb.ancestry.com/~ncomgs/tombstone.pdf
I was pretty close with my ad hoc advice, but they’re recommending a very specific “knife grade” epoxy, it hardens and fills in the damage, especially good for mower damaged corners and such.
Be very careful with Roundup around marble, too. It eats it over time.