Pinion nut advice


Pinion nut advice... twice now, my pinion nut has come loose, allowing the pinion gear to get sucked down into the pumpkin. You can see in the photos that the threads stripped clean out of the original nut. The second one was homemade, but still loosened until the final few threads stripped. The second time was fatal for the ring and spider. 
I’m getting ready to install a new axle and would like to prevent this from happening again. The shop manual doesn’t have a lot of advice. I’ve turned the nut down snug without impeding the bearings, then mashed down a couple of tabs on the king nut into the splines to keep it from spinning. 
What am I missing? Any other tips for rear axles & pumpkins on a 48 with mechanical brakes? Thanks in advance!

- Park


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