It's kinda funny, I was just talking to my wife about this myself, in case an over zealous LEO decided to erase my recording of the encounter once he discovered it. At the moment I use Tape-a-talk on my samsung galaxy tab. Since it comes with a device lock I don't have to worry about someone deleting anything from my device, all they could do is turn it off to stop it from recording more and that's assuming they can tell it's recording in the first place.
I do carry a normal voice recorder also, and have found some devices that will only let you delete files by pluggong it in to a computer, and then you'd still have to input a password to unlock the device. This doesn't prevent one from destroying the device outright but at some point we could become paranoid about it.
I will probably look at dropbox and associated apps. Maybe all you then need is a screen lock for your phone. If the LEO can't tell it's recording the 1 hour wait for it to sync on the interweb won't matter as much.
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