Some bad advice here applying a “no deeper than wide” rule to beach conditions. Wet sand with shifting density won’t behave like regular earth, and a pit at the beach is going to behave differently than a trench in regular dirt. If someone said they’re going to stick you in a 6’x6’x6’ pit surrounded by unstable wet concrete and let it go with you in the middle you’d probably say this wasn’t the best safety advice.