Nylocs if used correctly, will never come loose!!!!

Just make sure the nylon contact area is dry or free of lube.
By design they have a tapered insert and a reverse load to loosen them increases the friction more.

For the thrifty ones amongst us (including me) when they are removed lay them down on a hard surface with the nylon up. Give them a light peening with a hammer to swell the nylon slightly and they can be used many times over.