A nice feature of the Northland Shooter Supply action wrench is that it has a 1/4-28 bolt that screws into the action to prevent the kind of slipping mentioned. That way you don't end up clamping the action so tight it binds the barrel.

I use a two foot cheater bar on the nut wrench, and a dead blow hammer. Unlike Lizzy Borden, a couple of whacks is all it takes.