In reply to itsThere:
Get a ground anchor, available at most motorbike and DIY shops, and secure it in the garage.. the anchors can usually be secured to the floor or wall.. use a big chain through the bike and anchor..
OR
if you want a shed then put down some concrete blocks first, then shed on top.. ground anchor secured to blocks, big chain connected to anchor and up through floor of shed, through bike. safe and secure!