Harbinger, defensive posture, frost bar tab. Lots of stamina recovery to keep going. If you want to literally stand one place and don't move, immovable with 6pc heavy (don't add 7 or you'll self-root, it is inconvenient). The sources of block mitigation is cumulative, so 20% from passive and 30% stack, and you block base 50% and 20+30%, so 50%*50% = 25% instead of 40%, which is very serious boost.

Edit1: Be wary that bar switch created a spacing where you can't block. Time it carefully.
Edit2: And oh, the best skill in necro for this gameplay is Hexproof ofc. Because dots cannot be blocked, removing them for as little as 2k hp is a godsend.