Is your bike by any chance disc brake compatible?
Because if you have a disc mounting bracket on your rear hub, you can bolt a fixed cog onto it, and then you don't have to worry about lockrings, loctite, suicide hubs, etc.

If you can find one that has that option, pick it up.
REDLINE makes freewheel single speed hubs that are disc compatible, and http://www.londonfixiebike.co.uk/ sells some pre-drilled and super sweet cogs.
Or you can just get a cheap one and drill it yourself.
I'd recommend 16 teeth or more, as the smaller ones don't have the surface area for drilling.