Driveshaft center locknut

I've replaced the center bearing after it failed and now need to tighten the locknut back up in the center of the driveshaft. Problem if, I can't think of a way to stop the driveshaft from spinning. I've had a friend try to hold it while tightening and also tried clamping it lightly but it usually spins free. How did people tighten the damn locknut? Reinstalling the front half back into the gearbox is the only thing I haven't yet tried. Getting frustrated

 

i usually rattle it up untill it lines up with the marks before pulling apart

 

This^

Or a chain wrench.

 

BTW dont put the shaft in the vice and tighten it. To get the nut tight enough. It will spin the shaft in the vice. Tighten the vice up enough to hold it and you will deform the shaft.

Do what Eric said and clamp the flange