I've found a nice spot where you can get your defense skill up really fast at almost any lvl, we're talking 0-300 in a matter of minutes
These mobs in Barrens summon lvl 1 creatures that will attack you, the nice thing is that they never stop summoning so after a while there are hundreds of mobs. It really helps to have some kind of AoE to kill them after you're done but just running probably works also
What you're going to do is just aggro the mob, and then let him summon hundreds of adds, you can heal yourself if needed but since the little ones only hit for 1 you wont die in quite a while
Some screens:
Below here you can't see all the mobs since they are standing inside eachother.
Having a shield really helps if you're low lvl
Killing teh mobs:
That was all, enjoy!