I got the cog and lockring on as tight as I can, but under super hard backpressure, like slamming backwards, almost standing on the crank, which is not something I one would do in normal riding, the cog still slips. It moves the cranks less than 1/8th of a turn, but it still makes me uneasy. Should I be worried, and is there a way to fix the problem? I mean, it won't even move during a skid or skip.