Another Imolation type aura?

Okay, I guess I should expain what I am trying to do, then what I tried... so...

What I am trying to do is create two auras, each on a seperate unit, that can be affecting the same enemy unit. Both auras need to cause the enemy damage, while one also slow the enemy down.

I tried two differnt auras, the first was just a plain immolation aura, the other was an immolation aura, and a unholy aura with negative speed. It didn't seem like the immolation auras would stack on the enemy.

So heres the questions I have.
1. Is immolation supposed to stack?
2. Is there another base I could use for a damage aura instead of immolation? (not a percent damage, a set amount)
3. If immolation doesn't stack, and there is not oanther base I could use, could someone point me to a buff I could use for damage for a trigger spell that stacks with immolation? (not poison)

I think that is it. I thought immolation would stack, since if two heros had a cloak of flame I thought both would hurt the enemy, but it doesn't seem that way, but I hope I am wrong.

Perhaps the 'Breath of Frost' buff could be used? I seem to remember that doing damage over time...

Lightning shield cast by a dummy unit...if you can make it only hurt enemies

Neither of you know if immolation/cloak of flames stacks? I think that is the first thing I need answered for sure, I tested it, but I am new to this, so maybe I missed it working or something.

Nothing based on immolation (cloaks included) will stack with eachother.

The only thing I could think of was lightning shield, as a passive damage over time buff.