I have a laptop bag with a shoulder strap that I've adjusted to the right length, but over time it gets longer again due to bag weight. I'm looking for a hack to force it to stay in the same spot for my adjustment. The only thing I've thought of myself is to use a safety pin to pin both parts of the strap that overlap near the end to force them together in the same spot.
The kicker here is that my bag's strap cannot be removed from the bag. It does not clip onto D-rings, it's sewed around the D-rings on the end and sewed into a loop, so I cannot actually remove the strap to wrap anything around it (e.g. a rubber band).
Here's a picture of a similar bag with a similar strap configuration (again, not the exact bag I have but here for reference).