As above, if its knocked into the tab properly, its pretty impossible to come undone!? Are you being too gentle with your notch? This happened to me when i did my first bearing, thought it was 'locked in' enough but after about 10miles had loosened off. Re-torqued and bashed the feck out the nut so it was truely locked in. And that was 3+ years ago now and never had a problem since