Do you have a regular entryway door to the garage? If so, you can securely lock the garage door with a padlock - better than the flimsy tumbler lock built into the garage door latch handle. My garage door tracks even have a hole in the track for a padlock.

As an old retired firefighter I can tell you that an overhead garage door is the easiest door on your house to force. All it takes is a crowbar (we used to use a Halligan Tool) http://en.wikipedia.org/wiki/Halligan_bar under the door to force it up, and the locking bars bend.