A powerful watchdog should be restarted inside a timer interrupt.
This interrupt must handle several count down counters. If any of these pass the zero state then the interrupt was forced into an endless loop.
So any important process can have its own count down counter and must serve it periodically.
And different time out values can be supported, e.g. one routine must be served every 1ms, but others only every hour. Simply by using different reload values for any count down counter.

Peter