A hidden toggle kill switch. Needs to be fitted VERY properly though so as not to become a permanent kill switch
A bike alarm is not a good idea on an off road bike that’s going to get very wet and muddy all the time...
Basic rules are.. think that someone is out to steal it all the time...
Never wash it on the drive in view of people who pass by..
Become surveillance aware.. I.E. look for people who might follow you home, especially if you trailer it anywhere...
Keep it locked away at home, in an alarmed garage with additional security chain so when the alarm is set off no one will hang around trying to free the bike...
Make the garage so secure with layers of protection both soft and hard that anyone would give up and look for an easy bike to steal...

I carry a simple but strong and light weight no key cable lock for when I stop at petrol stations and leave the bike to pay or have a sit in lunch etc.. …. Cable it to a bike stand or one of the other bikes in the group… but always try to keep it in sight..
Enough to stop someone running up, jumping on and riding off before I could get to the bastard and re arrange his opinion on ever being able to have children…