Varieties of Locks

I understand that most ball trap devices rely on an honor system for the pull-out, which works fine for me. However, I recently discovered that even with a basic lock-pick and minimal skill, I can pick open the brass master lock included with my CB-3000… This somewhat breaks the illusion… So now I’m searching for something more robust; perhaps a standard pick-resistant model or a resettable combination lock would do. My main concern is ensuring that once I hand over the keys to my keeper, there’s no way I can simply open it myself. Any advice? Thanks!