A player on my server while going about his day runs over an auto generated stash trap and opens it up causing a trigger.

Can you please fix this from happening?

Seems a little sus. Is that the excuse he gave you? If you actually talked to him about it after only 1 trigger you messed up big time. Or how many times has he actually caused a trigger?

did you actually try this yourself? Why would someone be looking stright down while riding a horse, and then to go slow enought it opens a stash?

It seems that your player either inadvertently uncovered the stash by being within its reveal range, or they may have used their horse as a guise to cheat and reveal the stash deliberately.