I'd recommend one of these tied to the bike...
http://www.allposters.com/IMAGES/ISI/123965.jpg Seriously though, I had the same problem in my last house where a cat kept getting into the car port and peeing up the bike. I bought some spray from B&Q which worked wonders. Don't know what it's called (and I know that's not much help!) but it was a white spray bottle with blue/yellow label. You simply soaked around the area you wanted to protect and it kept the cats away. After six weeks of that (spraying every 5 days, which just about used the whole bottle) the cats break their habit and find somewhere else to mark.
antonye
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