A barking dog is about the best thing you can have to prevent a break in. Unless a thief is determined to get into your home for a specific reason (they know about something you have and are determined to get it), they will move on to an easier target. No one wants to mess with a dog unless there is no other choice.
Other issues:
An experienced burglar will always look for the easiest entry point. Why break in when there is an unlocked door or window?
Picking a lock is extremely easy in most cases. And, if the lock can't be picked it can always be drilled. Drilling a lock (referred to as the "rotary lock pick") takes about thirty seconds because the lock cylinder is made of brass which is very soft and yields rapidly to a high speed steel drill bit. Once the core is gone you insert a flat blade screwdriver and turn the lock open.
