1998 Chevy Truck Water Pump

Engine Mechanical problem
1998 Chevy Truck V8 Four Wheel Drive Automatic

I am changing out my water pump. The fan/clutch assembly is attached to the pump shaft directly by a 1" nut screwed onto the shaft. The problem is that the pump shaft is free spinning. How do you hold the pulley/shaft still so as to unscrew the fan/clutch assembly off the shaft.