The problem with hammering against the nut is that you could end up cracking the tab washer as it is too tight a bend. I too use a pipe wrench and never ever reuse a washer.
Lesson learn't many years ago when the fianl drive of the 1750 Austin Maxi was held on with a big nut and tab washer. Engine out and engine/gearbox split just to replace a 20p washer when ever they failed which they did on a regular basis. Having done it once to repair the manufacturers fault. You would not want to do it again because of your own incompetence