This is a good idea. Use as many walls as you can to protect your markets and wall off defenses around them. And as far as I am concerned, I would pass you by even if your mills were all the way in the corner without a single tower to protect them. You only need food for a few things and you'll get enough from raiding while you're already on a mission to find gold, if only to upgrade walls. Everyone's got a surplus of food. You only really need it more than gold a few days after you advance an age, up your barracks, then a few blacksmith upgrades and that it. Gold you need always. Leave the mills out in the open, let raiders have them. I hunt for gold in 99/100 attacks, maybe more, no exaggeration.