I like the double nut idea --- a 1/2 nut ( jam nut ) would be the proper way to go
You know that saying every action has an opposite reaction :
After changing the sprocket from 44 to 50 , I had to increase the length of the chain by adding 3 links and another master link , now the chain jumped off twice yesterday , got to figurethat one out ........ suppose to rain " bad " for the next three days