I had the LBS do it, and after it slipped I brought it to them right away to retighten, slipped again. I think ill invest in a quality cog and lockring (17t, suggestions?) and some tools.

Btw, If you have an 1/8" chainring, can you run a 3/32" chain? I know my chain ring is 1/8", dont know what my chain is, or my cog. Wondering what size I should get the new cog in.