I had pro Shaun Wallace tell me not to use a lockring on the track. If you tighten the cog well, it won't just spin right off. But if you crash, then it probably will, which could save your knees.

I have those hubs and a Surly lockring will work, although not with a Surly cog, because the Surly cog is too narrow to fit snugly with the lockring, and it'll slip. An EAI cog/Surly lockring works.