High PD kinda useless.

[Saxon]

Hmm, spamming forts along an active border and not manning them is a bit dangerous. If your enemy grabs one, they have a nice base to build from and you have to retake it at some cost. I prefer defending against with a more flexible border, where you can lose and re-take a province relativly easily. But as some one else wrote, if you have real problems on the border, you should have a real army to deal with it. Once you defeat the attacking force, you may wish to go and visit the enemy provinces for a little chat. After all, the best defense is a good offense...