Lvling my DH that way, only thing you need to use is caltrops to slow down those mobs. Wait with running until guard starts to run, spam slow, run the other way.
I guess every class has some stun/slow move (frost nova, blind, stun, grasp of the dead) so this is the best way to lvl up solo.
1-5 normal questing
5-25 a3 on normal
25-50 a3 on nightmare
50-60 just complete hell