My best results have generally started with the chainring. If it's an asymmetrical spindle I'll flip that around, or replace with a cartridge BB that puts the chainring as far inboard as possible while remaining on the outside position on the crank spider. Then I put a straight edge on the chainring, and measure from the straight edge to the inside of the dropout. I space the outside edge of the cog that same distance from the locknut, and re-dish the wheel.

fwiw I rode a fixed gear for years that was done the same way, on a road hub with a BB lockring, and never spun the cog off. But I did ride with both brakes, and I'm neither very large nor very strong.