tradtimbo

I'm assuming your question really is: "Can I get a lockring off without a lockring wrench?" becuas you dont need a lockring tool of any kind to remove a cog. cogs can be removed by a number of methods, the best probally being reverse rota-fix.

I'm not sure what you mean by having campy and shimano lockring tools but not having one for fixed. Shimano makes a very nice lockring, and I bet campy does too. You might be talking about freewheel or cassette removal tools?

To get a lockring off without a lockring wrench is diffucult and it still can be diffucult with a proper wrench. i suggest that if you think you'll use it more than once, go buy a lockring wrench. Hozan makes an excellent one. The one park tool makes is not as strong, and the teeth can actually break off.

If your set on removing the lockring without a proper tool you can try with tools you may have at your house. The first i would reach for is a hammer and punch. next I would try locking pliers with a concave surface and gripping teeth. the third option is a drill. the drill method is destructive, but if your not planning on using the lockring again, it can be done. drill a couple small, shallow holes in the lockring right at the notch and then give a few good whacks with a hammer and punch.

Good Luck!