I like the old lean on the spanners technique myself
You need to have a proper decent chainwhip or (a oil filter whip, which i have always used).
Stand with wheel in front of you cassette away from you .
clamp chainwhip on, hold with left hand.
put unlocking bolt in cassette and clamp with large spanner, hold with right hand.
spanners will be in roughly 20 past 8 position, as you look at it.
then lean on spanners.
Even the puniest of folk will undo any cassettes like this