Well, compression of the suspension usually works, but a couple of things; check to be sure that all the threads (nut and bolt) are relatively good. You could be fighting a screwed up thread. Also, if you put compression on it and it still spins, try putting a wrench on it and give the wrench some raps with a small sledge. This acts like an impact and should get you past the nylon that is holding you up.

And you may want to do axles with this method next time;

http://www.2gnt.com/index.php?d=Changing%20an%20axle%202

That way, you don't have to play with that nut.