That is sad, I did notice in that article it said -
"All you need is a photo ID to get a free metal detecting permit issued by the Department of Parks and Recreation, which grants permission to dig in more than 100 city parks. More than 500 permits were issued citywide last year."
First let me say I'd ideally prefer not to have to get a permit, free or not, but since that is what is already in place they need to be strict with those leaving holes saying the first time they get caught leaving an unfilled hole they will be fined $100 and their permit taken away for a year, and if they get caught digging without a permit after it being revoked then a $500 fine and permanent revocation. That would be better than simply making metal detecting off limits for everyone.