For sh*ts and giggles, I used a Surley "New" single speed disk hub (no lockring). I thouroghly cleaned the threads and used a liberal amount of red loc-tite to secure the cog, along with some hefty torque from a chainwhip. I never had an issue with it loosening in the dirt, but I certainly wouldn't trust it for "sweet hipster skids" on pavement.
When it came time for removal, I had to remove the bearings and use a mapp-gas/oxygen torch along with some heavy stomping on the chain-whip to get the cog off.
Yah - I know - Completely ghetto and not the right way to do it, but it was a fun experiment. Now that I have a new set of wheels, I'm going to re-install the fixed cog on my old back wheel so I can go fixed on occasion.