1988 Nissan Pathfinder stop engine from turnning

I've got to torque down the crank pulley/ harmonizer assembly to 95 lbs.? How do I stop everything from turning.(crank etc.) Also , is there a "woodruff key" directly under the bolt and washer that will be torqued back down. It originally backed itself out due to super overheating issue. Car was stopped before pulley left area.
Thanks
Peter