I don't usually post on this forum, however, your topic peaked my attention. I have lost two micros so far (one by the "cache pirate") and I know others who have recently lost 4. This seems to be a problem that is expanding and has the potential of growing even bigger and getting out of hand.
I agree that there are some which are lost to the enviro-nazis and there are those who stumble upon them. I do believe that those taken intentionally are at most done by just a few people. I can't believe that there are a large number of people who would take the time to go take these caches (I lost one micro which was a 2 mile round trip deep into the woords).
So far, this as such, is just a pain in the neck and takes away from the sport. My concern is that this will expand and people will start getting hurt. Either one of these snakes-in-the-grass will rig a cache to cause property or personal damage or someone will catch one of these individuals and beat the tar out of them. Neither scenario is good.
Solutions: One person told me to just keep replacing them and hope who ever is doing it will get bored. Another told me they were going to lay in wait and spring some sort of trap (not practical or safe as far as I am concerned). Then of course there have been a number of good suggestions just on this list.
I think I will probably keep replacing them. I have thought of making them premium member caches. I probably will keep replacing them hoping the "maggots" will just get tired of doing it.