To sum up, the goal is to REDUCE the possibility of theft, you will never completely remove that possibility. A thief prepared enough can take anything. What you are primarily trying to do is prevent a theft of opportunity, and deter that theft.
Case in point, most people have a wooden shed behind their house. Most have a padlock or two on it. The theft of opportunity is prevented, most thieves would see the padlocks and stop there. A determined thief would plan out the theft AROUND the padlocks, taking a sledgehammer to the padlock hasp, or knocking out the hinges, or taking a chainsaw to the wood walls and make his own door. The good news is 99% of the thieves out there are thieves of opportunity. Determined, professional thieves are more rare.
So - do what you can to stop the thieves of opportunity. The pros you can't worry about, they will go around your defenses.