Two large screwdrivers work well to pry large clumps apart - easier than a knife, IMHO, as I have broken knives trying to get clumps apart! The plus side of screwdrivers is that they don't damage the plant quite as much.
There is also a dividing tool ( no commercial interest in this!) that some people swear by. Sorry, I don't have the link but know that my buddy Nikki Schmith made a Utube video about it!
