Suspicions don't hold up in court, you have rights, you just have to be aware of them and know how to exercise them. If you lock the car, what can they honestly do? Search you for locking your car?
A great deal of people have a misconception that cops can actually do a lot of things in terms of jailing someone and finding evidence. In face, they can't, most of it relys on the consent of the citizen, which you don't have to give. ie. searching a car, or breathalizer.