my acs kept loosening off, so i took the lockring off, cleaned the threads on the lockring and freewheel body, applied some threadlock, tightened the lockring up, and left it overnight.
after this, it never loosened off again. most people probably slap a big amount of loctite threadlock onto dirty threads, and ride straight away. never works.
eno freewheels seem to be pretty good. if you find a decent rear hub, front freewheel is really nice...