Nothing to do with Halloween but wanted to share this. I needed to redo a toad habitat and wanted it to look like rocky outcrops of old coral rock, like the kind you find down in the islands. I reused some old, resin live rock props lying around but had to modify them. After cutting in halves, I filled in the gaps with sprayfoam and smeared gorilla glue over it. Spraying a lot of water on the glue will cause it to foam up outta control. This is why I love this stuff. The gorilla glue forms a hard shell over the foam and actually resembled the resin of the rest of the prop. What really surprised me was the painting redo. The original paint job was purple and pink blotches. I covered first with white spray paint followed by black, then brown, then green washes. It looks like old coral you can find in the woods down here and in the Caribbean.
The bottom half of this one is the foam/glue shell
Closeup of the gorilla glue shell
So I'm thinking this technique can work for a tombstone prop if it had to look like carved limestone or coral rock (like a pirate's grave), or if you need some bones to look deformed or ossified like in a cave.