On my machines, I only know half of the key for file server, the other half was set by my lawyer (He lives down the hall from me in my building). I also fix some of his systems, and as such, I have a couple disks with highly-sensitive information on them (I have all the proper NDAs and contracts set up to allow me to posses such things). So in order for the police to get at my data, they'll need to get a warrant for me and a subpoena for the lawyer, in addition, they'd have to get a third party involved to ensure that the evidence they are gathering doesn't violate the rights of my lawyer's other clients. Any wrong step by the police and the full weight of the ACLU and several other lawyers will come crashing down on them.
The volume locks on reboot and it just so happens that the power cord for the file server is under my desk, where it can 'accidentally' get tangled up around my foot and pulled out when I get up to go answer the door when the police come knocking...
I do have the advantage of not having done anything the police would want to come talk to me about, but I'm not going to give up my data without them going though the proper channels and making sure they've dotted every 'i' and crossed every 't'.