I have heard that outboard theft is increasingly common especially on places like Windermere and the Norfolk Broads. To bring things closer to home for me, outboards were taken from boats stored for the winter at Ullswater Sailing Club last year.
I have gone for a belt and braces approach with a clamp lock and registration of the outboard with Datatag. I have also purchased a Norfolk Police outboard cover (pdf flyer attached), the idea being that you take off your cowling and replace it with the cover. Talking to Martin Chapman from Broads Beat, the only theft associated with a cover in place was when the owner had left the cowling on underneath the cover!
It has certainly given me some extra peace of mind this summer and thought it worth a quick post in case people have not come across the cover