[Asbostos]

It's not that bad. The undersea environment doesn't suffer from erosion and weathering which basically prevents any long term construction from surviving very long on in the air. If dolphins carved words into the sea floor using a tool, they could easily be very long lived.

[rm_-rf_slash]

What would the tool be made out of? Would any rock do or would it have to be a specific type that requires modification? What would they hold it with?

[eru]

Why no erosion? There are still currents.