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
The way to remove it if you haven't got a oil filter wrench:
Lay old chain on ground.
Lay folded up sheet couple of layers thick on top of old chain.
Drive vehicle so that middle of tyre is resting right on top of chain, i.e. so that chain can't budge.
Place other end of chain over cassette in such a way as to prevent it from freely rotating the way you're trying to turn it.
Get lockring tool on cassette, and adjustable spanner on lockring tool. Wedge bike wheel against vehicle's wheel (while on ground vertically and perpendicular to vehicle's wheel). Such that pressing down on spanner will turn spanner anti-clockwise.
Turn spanner, if necessary by attaching length of pipe to it to get more torque. Job done.
If you do have oil filter wrench, steve austin's method.
Blimey bonj - that's a fair bit of work, but that's one way of holding the 'wheel' in place.....
If like I've have had in the past, a seized 'old' freewheel that wouldn't come off so.... freewheel remover attached to a large spanner, attached to a garden rake for leverage - it eventually gave way and I went flying backwards down the drive......
it's not that much work. think about it - the amount of work isn't proportional to the weight of the vehicle, is it.
I've used a tool that consists of an old chain wedged down some old mtb handlebars, essentially like an oil filter whip with a big handle, and been (almost) unable to do it by wedging it under a washing machine when it lifted the washing machine up. Although to be fair, Steve Austin's method sounds like it could be effective, if you can get the filter wrench and the spanner in a good enough '20 past 8' position to get the right leverage.
Access to a good solidly mounted vice could be the answer.
I removed a freewheel effortlessly a while ago...clamp the removel tool upright in the vice, slide the wheel / freewheel onto the tool and rotate the whole wheel...masses of pull and grip.