Just wanted to chime in here and say, if you do go the external watchdog route, don't use the Deep Reset Tutorial posted above if you want maximum reliability.
The EN pin has an inherent flaw, whereby it locks up the Boron if anything else that attaches to the boron can backfeed more than a minimal amount of power. Lots of sensors and circuits backfeed enough power to allow the Boron to be locked up this way.
I think @rickkas7 should post a warning on that tutorial and Particle should post a warning on its Boron data sheet. Knowing this could have saved me $10K and a week of my time!
We have around 100 Borons in the field (and 1000+ electrons) in remote locations all with external hardware watchdogs. I think you may be spinning out here -- If I were you, I would go back to the drawing board on your project and implement a proper hardware watchdog. Sorry if this is a painful message to hear.