The frost atronach is great for blocking tunnels, just make sure you don't get caught on the wrong side of the tunnel cause they can block your escape if you do that . . .
Right - I've gotten good at casting the spell in the direction I'm running and getting through the black and blue 'void' just as he appears so he ends up behind me. In a worst case scenario, if you he's blocking my path, I'll re-cast to a different location and clear him from my path. Mongo is a buddy.