Here's an idea for hiding a geocache. Prepare a container with a secret compartment. Fill the non-secret compartment with trinkets and a fake log book. Put the real log book and the real trading items in the secret compartment. Hunters will find the container, thinking they found the cache, and quit looking. (Alternatively, prepare two containers and hide one, the fake one, in an obvious spot, sure to be discovered first.)
You still have to prevent the hunter from logging a find. Require the finder to supply a secret code to log the find. Put that in the secret compartment. This works better with those listing sites that support secret codes (like gpsgames.org or tc.com, which calls it a confirmation codes), but it can work with any site just by announcing the requirement to supply the secret code in order to log the find.
I suppose some hunters will insist they found the cache and the code is missing. If you are willing to p*ss off a few people who won't accept your insistence that they really did NOT find the cache, this idea could make for a devilishly hard find.
Let me know if you try it, or know of cachers that have tried this already and how it worked.