Taking off a lock ring and cog without a chainwhip?

Needle-nosed pliers will not tighten a lockring sufficiently.

A good chainwhip/lockring tool is only £25 and is well worth the (small) investment if you ever change cogs. http://www.hubjub.co.uk/etc/etc.htm

+1 hard to believe how many times I (and others) have used this thing.