I would love to do a tv programme called "Scrotewatch", like Badger Watch but instead of food to tempt them, a nice shiny MTB left outside the local leisure centre overnight, locked up but otherwise vulnerable and watch them scurry from under their rocks to either nick it or to wreck it, set fire to it, anything to make sure its not there or usable for you in the morning.
I dont know where this comes from in the British psyche, other countries in Europe I suspect it would be safe, its almost that the scrotes have to do it, part of their make up, even if it inconveniences them, as in oh damn, I am already late but some bugger has left a brand new bike I am obliged to stamp all over.