A lot of items I notice "go missing" are because of new cachers. They might not be familiar with the "rules" or they are just starting and really dont care, if they see something they like, they take it. I guess they dont realize the efforts and disappointment of the owner should it be taken. I always like to keep an eye on my tb's and will send a friendly note if I see its inactive for a while. While this doesnt help all the time I think it may a little.