[atul]

"He gets a few of my province defense 1 border areas."

A tip that works only against the AI: It seems much of their decision who to attack depends on the apparent power and difficulty to attack bordering provinces. Setting PD to 1 on border province basically invites an AI nation attack. 11 or so should prevent some, I've noticed that with PD of 21 or higher AI rarely attacks.

Anyway, only in SP. In MP, PD above autopatrol (10) is usually waste of money, many times PD of 1 is perfectly viable.