buy some loctite red. rotafix your cog w/ loctite to the hub... get a lockring wrench w/ a long handle.. or use vicegrips on the end to extend the handle for more leverage... loctite the ring as well... let the bike sit for 24 hours so the loctite can cure... the cog will never slip. i did this on a suicide hub setup.. and never once slipped my cog ...