Province Defence?

[Loren]

PD works wonders against the AI.

I generally put 20 everywhere to keep from losing provinces to spells and almost all random events.

Beyond that, chokepoints are a wonderful place to use it. I've put 125 in a choke point and quite a few troops besides--and an incredible number of AI troops died against that barrier. I was killing over 100 units a turn there for years.