Arighty, here's my solution.
First, get some cheapbike you won't really need. A used one perhaps. Clean it up and make it look nice. Hook it up where you usually hook your bike up. Now, use a setup that looks real easy to saw through, break, etc (ie. some crappy looking wire/cable and lock). Now. The padlock is really an electoronically detonated explosive (not too much, but just enough

), and the cable is the trip wire - as soon as it's cut, off goes the 'lock'. (Very simple circuit design, along with the detonation setup.)
Soon, that will be a very safe spot to leave your 'real' bike.
Problem solved.
