Techniques - Loosening rear hub nut
Hehe! Psychonaut there appears to be tightening not loosening, but you get the idea :)
Whatever though, it isn't a bad idea to keep the wheel on and with full weight on that side (jack t'other) lock it up somehow, because stopping the axle moving is half the battle...
Breaker bars Vs T-bars
Rather than break a breaker bar (3/4" bars can be broken!) the correct tool for loosening and tightening is a 3/4" T-bar and 3/4" drive 46mm flank drive socket (although 3/4" bi-hex sockets are frequently supplied for this job and will do) A pudlock to extend the T-bar is often needed (a pudlok or putlock is a 5' scaff pole flattened at one end)
EMPI style Impact wrench
for removing difficult hub-nut easily, not recommended for torqueing back up.
Grinding and chiselling
Another way if the rear hub-nut is really stubborn: angle-grinder, skim but do not touch threads. Then sharp cross-cut chisel to split the nut off. Threads are very fine and easily damaged. Heavy dolly under nut if chiselling down. Else chisel across to stretch thinned area open and break nut/thread bond.
New nuts from Just Kampers (£4-50)
Heat (gas burner or carburizing oxy-acetylene flame) is sometimes used, but should be used with caution.