It takes a snarfer to catch a snarfer. Or almost so. If your bluetooth cannot be switched off most of the time, then your device is prone to a bluesnarfing attack.
The best way around this is to know when you're being bluesnarfed. There are several softwares which you can use for this. Most of these are simple tools that helps detect any bluetooth connection between your phone and other phones.
While bluejackers and bluesnafers use these tools to find devices to attack, you can also use these tools to see if there are any unauthorised pairing of your device by other devices.
These tools include "bluesnifff" "easyjack" "bloover" amongst many others, most of which can be found in bluejackingtools.com
Hope this helps