I drill out my bolts and put a bent piece of wire in to keep them from turning out. Works for me.

I also ditch the gaskets and put a light smear of the permatex ultra copper gasket in place.

On some mufflers the bolts are recessed so you have to rely on some type of lock tight goop.

I use permatex ultra copper gasket on those, and the lock wired ones. No problem, as mentioned clean the bolts first, I use paint solvent.

Nothing like watching 150 bucks of muffler disappear into the weeds, anyone been there