My mate who sub contract for vw leeds and leeds audi attends both of them at least once a day to sort the damage out due to stolen navs. Huddersfield & Harrogate vw and audi used to be bad for it but Nick was telling me they keep all the cars with navs somewhere else or take the units out when they come in on part ex.
Its a pee pore world we live in and there will always be scum doing this sort of thing, but as long has your vigilant and park your car in a well lit area or secure carpark when your out and put valuables out of sight then thats the best you can do.
Darren