I bought this set of special tool on ebay when working on my cooling fan last year. After many days trying several different ways (dead blow hammer, PB blaster, WD-40 ... ), I almost broke 1 of the 4 water pump mounting hex bolts.
But then I drove the car to a local auto shop and they removed it for me for $20. I didn't see the tool they used but they told me it's a type of air impact wrench. This method is cheap and much safer for a tough clutch nut. I guess the fan clutch on my car was not removed for many years before that (bought in summer 2009). I put on anti seize compound to ease future removal.