Our garden door would open itself a few centimetres if not locked from one side or another. This causes draught, escaping dogs and all kinds of unwanted by-products when we are just in the garden for a bit and don't want to lock the door from the outside.

This bracket keeps the door closed but stille easily pushed open. It uses flat round 20mm diameter neodynium magnet with a hole in the middle. One os affixed to the door and another glued to this bracket. The door is closed and the bracket screwed into place while held in the correct position by the locked door.

The magnet in the bracket is held by 1mm of plastic so that the two magnets don't slam together. If your magnets are too weak, you might want to reduce that distance.

Shetchup source included.

UPDATE: Added version 2 which is a bit smaller on one side and has a lid to cover the mechanics. Version 2 Sketchup file includes the version 1 design.

Depending on the strength of your magnet you may want relatively high infill to keep the bracket from deforming over time. However, correctly mounted there should be little stress on the bracket most of the time.

Put a bit of glue in the magnet hole of the bracket, put in the magnet and keep it in place by resting the other magnet on the other side like it is supposed to be when the door is closed.