How to explode a hard drive

I know this isn't strictly tech, but I felt it's the best place for it.

People talk (on 4chan and such places) of raids by the police on their house to recover hard drives due to suspicions of CP or of pirated content.
I was wondering if anyone knew of a case where someone actually managed to destroy their Hard Drive, either remotley or before anyone could get to it, or any stories of the sort.
Could it hypothetically be fitted with some sort of... remote water filling thing?
Post anything relevant please.

I actually use a seperate wirless "node" for housing of stuff (not CP mind you). I hide it in a wall safe of sorts, the safe is made of a special plastic that's nearly as hard as steel, (Odds are the feds would use powerful metal detectors all over the walls if they suspected a hidden node) this works twofold. 1) Getting into that safe would be very, very hard. 2) The plastic outside stops the metal detectors from sensing the metal bits inside. To minimize the total amount of metal the server has I don't use a case.

The server only listens to my computer, actually my NIC - when it gets the signal from my nic it broadcasts. (No Active Broadcast, way to easy to triangulate) I get the data I want from it making sure not to store it on my computers hardrive. It uses a deadman switch as >>101 said that needs me to check up on it every 13 hours or else it turns the content of its hardrives into garbage. (I considered some kind of remote super-magnet, or small explosive but ruled that out. I can have SOME kind of plausable deniability having a server mounted in my wall, but if it's blown the fuck up, I think not).

Overall, A project like this would cost you about 1.5k, the price increases as you house more hardrives. Most of the cost comes from buying the safe, and getting the tools needed to drill the holes into the damn thing. (You need holes for power\wireless antenna).

Also, being able to fix sheatrock is a big plus