£16 Rear hub noise

My 1991 316I has developed a knocking on the rear nearside wheel which tends to also develope into a rubbing noise (as if the brakes are rubbing)
my local garage (not a BMW specialist) has fixed it twice, saying it was a loose hub nut.
It has now re-appeared, so they obviously haven't got it right.
Surely there must be some form of locking device on all components to stop them coming loose?

Any ideas please?

Thanks in anticipation

Dave Elsy