Ways of responding if you HAD left unfilled holes on a beach:
Explain that you were doing a public service by removing potentially sharp metal objects from the beach where kids play and people tend to walk barefoot, and simultaneously giving children a headstart on any sandcastles. Kids of today have such short attention spans, they can't concentrate long enough to build a sandcastle from start to finish.
None-the-less beach sand is a serious trip hazard as the uncertain footing could lead someone to fall, get sand in their cossies and suffer a crunchy-crotch injury. You can't be too careful, lifeguards are being instructed to place their flags not in dangerous surf but instead in a controlled clubhouse environment behind barriers to prevent people getting near them - they are a trip hazard too. This also has the effect of reducing the number of drownings and ensuring swimming only takes place on non-slip surfaces while being supervised by trained first-aiders.
Perhaps it should by legislated that you must detect in a life-vest just in case.
As a rule, always fill in your holes, even in rivers and dams, swamps and (from another post elsewhere here) sporting ovals.
