If you're not already running your cord up over the back strap button, do so. It's the twisting and swinging of the cord that loosens the round jack more than anything else. No swinging = no loosening.
I always drip super glue around it very carefully. If I need to get it off, I heat it up and use a little elbow grease.
Teflon tape also works.
The right answer though is definitely electrosocket. I even went as far as drilling a huge hole in my G&L ASAT for one. Not because it was coming loose, but because it kept shorting out. It was one of those long threaded jacks held in with a thread, and it was a nightmare to access. Problem solved.