hmmmm that sounds like an imposibility, you can only plunder ONCE every 24 hours, if he is plundering 3 times a day then that is a matter for the mods, report the fact and give proof (screenshot of log) and that player will cease being a player.
I have got the majority of my blueprints from plundering, and also suffered from being plundered from higher players, time your production, and use a decent defense, these are the ONLY ways you can avoid it.if you lose the coins from one house it doesn't matter, its a trifle, but arrange your production so you KNOW you will be online to get it.