Shaun Wallace, a long-time British Track pro who was a sprinter/kilo/miss-n-out/points race kind of guy (not an endurance trackie ok) and I met at T-Town once. He said not to use lockrings on the track. He said that as long as you torque the cog down enough it won't spin off during anything you do on the track. I followed his advice and found this to be true. In fact he said, the only time it will spin off at all is in the event of a crash, and he advocated no lockrings on track to save your knees and legs in the event of a crash. I rode the same wheel on the street a couple times, and I was fine, it didn't slip, but I was riding with a brake and not trying to skip/skid.

Conclusion: Track: no lockring
Road: lockring please