I have a similar problem as I don't have a lot of land to work with in my backyard. I make sure that any firewood that I store near my house is elevated and placed on metal racks. I have read that termites don't really like walking over metal. I put all of my less expensive wooden 2x4 racks on the perimiter of my property at least 25-30 feet (or more) away from the house. There are a lot of termites where I live, but I have never seen any on wood in my racks (wood or metal). I have seen them on stray pieces of firewood that are left in direct contact with the ground, where it is moist.