How do World War II-era bombs end up in suburban backyards?

Auckland residents were evacuated from their homes last week, Stuff reports, after a gardener dug up a mortar shell from the World War II era. The Defence Force was able to safely dispose of the bomb – but are there more out there? Similar items had been found in the past, in varying states of explosive safety. The Explosive Ordnance Disposal team has responded to more than 80 call-outs so far this year. A police spokesperson “encouraged” anyone who located anything of concern to contact Police on 111.