Laser cut electronic servo-locked box
This is a design for a box that you can laser cut and glue together to create a reverse geocache.
The lid slides open and is prevented from being removed completely by two small bolts near the back of the lid. This also covers the hole that the latch fits into. This prevents the latch being inserted when the lid is open.
The servo lock mechanism is designed such that the servo can move into the locked position when the lid is open without preventing you from locking the box. This means that you do not need power to lock the box. Simply move the servo to the locked position immediately after unlocking.