1995 Diamante crankshaft pulley removal

[fray97]

My brother has a 1995 diamante. For whatever reason he has his timing belt off and trying to take off the crankshaft pulley. He is having a hard time getting the nut off to take it off because the pulley wants to turn. He may or may not have already bent his valves.

What is the easiest way to stop the crankshaft from turning while loosening this nut?

Also I cannot see the tick on the pulley for setting the time. Is it on the larger side of the pulley or the small side next to the engine?