Red Loctite is a valid substitute. Make sure the threads are clean.

If you're real paranoid you can GACK the bolt thread. That's an engineering term for taking a punch and a small hammer and folding a portion of the first thread over on the bolt.

No I ain't kidding. We do it all the time on multi-million dollar rotating machinery balance weights to make sure they don't back out. You may need to use a die to restart the thread later depending on the bolt grade and GACK severity.

Regards, Kitz