It might not deter the determined thief but I have modified the spare wheel carrier by removing the hook and welding on a 40mm long extension to the hook. It needs to be angled in so that the distance between the extension and the body of the hook is 10mm. This ensures the cradle can only be released from the hook when the bolt is completely unscrewed. I've just modified my third one and it's a simple job for anyone with a hacksaw and a welding kit. Your local friendly blacksmith perhaps. I am amazed that Citroen can't introduce this simple mod but considering they can't even get the basics right, I'm not surprised.