[ceremony]

(1) Threaten something of his that is more valuable to him than the damage he is doing to you by rampaging through your provinces, and hope he needs to use his rampaging army to counter that threat.

(2) Make sure to recapture as many provinces as you can without confronting his main army. If an enemy army gets loose in your backfield, there comes a point where he can't replace his losses (unless he is reinforcing himself with flying units and/or summons, in which case you're in trouble) and you can make a loss in battle catastrophic if he has nowhere to retreat.

I had a situation where an opponent built a lot of temples and my response was to build a large army and break through his lines on a temple-razing mission. It worked for a while, but he kept building enough province defense and scratch recruits that I'd lose a few units each battle that I couldn't replace. Eventually, he assembled a large enough army to defeat my force which had been reduced by this attrition, and I had nowhere to retreat when I lost.

I think I plowed halfway across the Orania map on that run, though, so it cost him a lot of money in province defense and recruits to slow me down to the point where he could defeat me. In the end, the result was trading a large army and my pretender for about 10 razed temples (2000 gold) plus the cost of his PD and recruits. I think I came out on the short end.