[Van down by the river]

Mantis shrimps Stomatopoda, have a thin carapace similiar to Lysmata grabhami- Cleaner shrimp. Logic would state that some of the larger species due to their size would have a thicker and harder Carapice.
Some species are quite large, up to 38cm ( I couldn't find anything bigger).

Rather than hot water, destroying other organisms (sponges,etc) which may have a negative effect on water quality. Maybe try the pointy end of a zip tie, sewing needle,nail or other hard/flexible object to "spear" the holes in the rock.
I have heard of success with the starving method as well. Their lair can often be found by debris. broken shells,
sediment ejected while cleaning their den, or previous victim remnants.
I have also witnessed them use small stones or shells to cover/hide the entrance. If you can catch them alive they make interesting animals for a small species tank.