Peter,
We only had one bike go missing and that turned out to be a drunken misunderstanding on the taker's part. It was returned the next day.
We usually always lock them if they are where we can't see them. If we use them at night, we don't leave them anywhere obvious. That is about the only things we do. Perhaps we are lucky but we often go shopping with our bikes, forget to lock them and leave shopping in the basket as we go from store to store. Have never had anything go missing. Maybe our bikes just give off good vibes. Who knows?
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"There isn't much to be seen in a little town, but what you hear makes up for it."
Kim Hubbard