It is also needed a value rock_sounding (or rock_acoustic or similar) for rocks known through History for their acoustic properties (such as producing big echoes, so people used to believe those rocks talked). In Galicia and other places of Atlantic West such as Ireland, Wales or Scotland there are a lot of rocks known as talking rocks and also litophones
Yes, do it! Tags dont have to be on the wiki before use.
For the value I recommend a typical english term, because other values of archaelogocal_site are used like that. So I prefer =litophone or =sounding_rock over =rock_sounding. As I am no native english speaker I might be wrong about what is used typically in english.