The design of these simple boxes with baffle on top haven’t changed much in 45 years or so, since USFS Campgrounds had them for fee stations near entrances.

Part of the design flaw has always been a lack of intricate mechanism, of weights, springs, a few more flaps that work only One-Way. Jr High or younger kids were known to have been using coat hanger wire, cable fishing leader, and actually fishing for envelopes in the early 1970s.

No actual hooks were used. A lot of ‘hand’ and a bend in hanger wire was the earlier method. Appears there are a few mild angles, into the box. Nothing too hard. 

One enterprising young man waited until his dad, a USFS boss, went on vacation; he asked to stay home to watch their house. With the extra sets of keys, he had a green car, special fuel pump, & keys to those lock boxes. And beer free money for a few months; plus the use of a car or sometimes a truck.

The son went to college, is paid well, now is a head republican, in MT state. ;)