Tenant retaliating by shutting off power in breaker box

[Mervin James]

Hello BiggerPockets community. I own a duplex and live downstairs. For a variety of reasons, I am wary of the upstairs tenants shutting off power to the property using the breaker box in their unit. What can be done in the case that they do? There are switches in their breaker panel that directly control power in my downstairs unit. I need to mitigate the damage that may be incurred if they do, or simply prevent them from accessing it. 

It should be noted that I live in a very cold climate, and having the power shut off for any part of the property will result in whatever is inside to freeze — including me.

[Nathan Gesner]

Report them to the police, every single time. At the same time, start the eviction process.