How do you get the offense and defense to survive past level 8-9?

I keep getting to that point and then you run into things that smite, or fireball, or otherwise deal huge amounts of damage.

Last game I thought I was set up pretty well, rings of various things for protection to swap in and out, but in the end some freaking @ with fireball popped up while I was resting from a battle with a Yak and it was all over.

I seem to go fine...fine...yea..kick butt..good...BLAM. Freaking wasps have killed promising characters a couple times with their damn immobilization poison.