Search for rotafix - some will poo poo it, but I stripped a hub that I broke a chainwhip tightening the cog on (broke it because I couldn't tighten it any further by hand), and have tightened with a chainwhip as much as humanly possible with plenty of grease on the threads, and gently rotafixed the last two cogs I've put on, and they haven't budged, one in 8 months, the other for a year. Under a heavy rider who rides downhill to work every day.

A lockring spanner like the Hozan makes lockring tightening *much* easier than one of those bb lockring spanners that you get in e.g. the nashbar or performance cheapo tool kit. You need at least one chainwhip no matter what, so for fixed gear stuff, you might as well spring for the lockring wrench as well, as it's the only fixed-specific tool I can think of.

There should be a rotafix sticky or something, it's the best tip I've learned here.