Make spellgems that are spelltraps not visible to anyone not on the targets list who is not the setter.
(So like the person who set the spelltrap can still disable it by picking it up, but if set to e.g. non-faction faction members will not be able to see the spellgems)
Edit: Really just anything that prevents non-targets from yoinking the spellgems would be great because it's really frustrating, easy to exploit and with zero feedback I have no idea whether it's working or not or who to convince to leave the spellgems on the ground.