I'd suggest that it should be possible to dig up corpses. But
- maybe only those who were witnessing the burial would know the place where to dig - they could pass it on somehow, maybe by starting a project for digging up a corpse and others could join.
- The resources buried on a corpse would gradually vanish, and the items would deteriorate on an increased speed. So after a while there would only be a skeleton, and finally nothing at all.
- Steel items could be unaffected and keep their normal deterioration rate since I don't think it rusts, at least as fast as iron.
- And maybe random digging might be possible, the chance of hitting a grave depending on the amount of corpses buried on the region divided by the size of the region.
(This was in general discussion but goes for necroing this thread.)
I would also add that accidentally finding buried items while digging for sand, stone, clay or another substance should be possible. The buried items would be saved in invisible "containers" that would be destroyed after all has deteriorated. Thus you couldn't find items endlessly but only things that have been buried in the past. And once an item is found and picked up, it cannot be found a second time unless buried again.
Burying items without corpses should also be possible, but that's another thing. And putting them in chests or other containers or wrapping them in cloth would slow down the deterioration rate.