1. Like BY BY said, Change the frequency of your garage door, the new ones dont use dip switches so your one must be the older type. Just look up the manual or call someone to come over and change it for you. Another suggestion is to unplug the thing of a evening and just just a few garage door locks to keep it closed. I suggest the sliding door locks.
2. Call the police, tell them whats happening. Its their job to look out for you and they may be able to help out. Its also good if you told them just incase something happens later.
3. Sensor lights are your best friend, another suggestion is to get a simple alarm system for your garage, perhaps a few screamers with a motion sensor and a remote arm switch. You could get this from jaycar or an alarms reseller.
4. Tell your neighbours just in case they dont know, and give each other your mobile numbers. Neighbourhood watch works people.
5. Big dogs are cool, but easily defeated like in the movie Fletch.