Instead of the key rings that are split and you can slide keys or tags off with your fingers what about using something like a small chain link that you can squeeze closed with pliers and would take two pair of needle nose to open back up?
Or some small mini metal "S" hooks like these:
www.amazon.com/LASSUM-Connectors-S-Shaped-Hanging-Jewelry/dp/B07QJXFZNW
