One solution might be to keep him so busy responding to YOUR attacks and YOUR raids that he does not have the time to do this.
Oh. And people really should have more than one fort and a lab before this happens. Dont wait for the raiding forces to start coming BEFORE you invest in defense. Prepare for it ahead of time. Make your border provinces and chokepoints MORE than 20 PD by whatever amount you need to STOP such attacks.
If you wait till 11 raiding forces are coming in before you begin to make preperations to stop such attack dont cry cause really, its not the games fault you suck
