I dunno, I really see it as a cheap solution. I mean, Sisohiv has already listed a bunch of other ways to prevent looting, which actually are built into the game for those reasons. Not only that, but it's completely unrealistic.

I understand that turning off the marketplace is an inconvenience, expesially of the attackers are going to take a say to actually get to your city, but having it be a researchable technology or having units specifically for that purpose would be a lot better than nothing at all. At least that way, the attacker would have to do some work, and not all of the resources would be looted. Sure, it's sort of a lose/lose solution, but it seems quite fair to me.