Driveshaft nut is gonna be the death of me

Easy - weld a big nut, or a socket, onto it. Always works.

By the way, the way to get them off is with a 5 foot extension on a tommy bar. Also suitable for tractor driveshaft nuts.

What car is it and which side is it on?

Some cars have "handed" nuts...in other words the nuts on the drivers side undo in an anti-clockwise direction to prevent them from working loose.

I'm not saying this is the reason for your problem but it's worth checking.

sPoNIX

Single hex, threequarter drive socket with tee bar and a length of scaffold pole, plus a helper on the brake pedal. Works without fail.

mrcheerful

without stating the obvious, are you undoing it the right way? next point, what car is this on? which side? and to stop this happening again, you put the spanner/ratchet/whatever onto the hut brace it with lots of bracing stuff (bricks or something piled underneath it) and then drive the car forward/backward (depending on which way the nut undoes) to crack it job done, and no hassles :)

Think the easy way now would be with a very large Stilson - it's a self gripping wrench. A decent hire shop should have one - I'd go for one about

3 ft long. And make sure you're undoing it the right way as others have said - if you can see a bit of the thread you should be able to work it out.

================= Since you appear to accept the idea of destroying the nut (make sure you've got a replacement in hand) use an angle grinder to grind PART WAY through one of the flats. This usually weakens the nut sufficiently to undo with the correct spanner. The heat generated by the grinding also helps provided that you don't overdo things!

Cic.