Think layered security:
1. Out of sight, mostly out of mind. - Cover it or put it in a garage.
2. Theft deterrent. - Alarm or lock. Use something that makes lots of noise. Thieves hate attention.
3. Financial loss control. - Full coverage insurance. If they want it bad enough, they will take it anyway.
As I usually tell friends, the alarm is for the amateurs. Insurance is for the professionals.