I've read that one should NEVER ring a fire with rocks because the rocks may have absorbed moisture and might explode.

Other places I've read that one should ALWAYS ring a fire with rocks, to help keep the fire from spreading in an unwanted manner.

From the members here, which advice is correct?
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Ors, MAE, MT-BC
Memento mori
Vulnerant omnes, ultima necat (They all wound, the last kills)