OK, this darn barn is on a minor slope (the whole block slopes). The lower side has somewhat washed out leading to other problems (rot, sag). The original foundation is mortared stone, but I'm pretty sure there's no footer. I'm not even sure there's an up-slope foundation on the other side; for certain there's water flow, as this is all downhill from other things, and sending the water someplace else isn't much of an option.
My thinking is that when I replace this foundation, I should treat it as a retaining wall, and make sure it has weep holes, a french drain, and the like. Smart? What else can I do to reduce the wash-out and keep the problems from spreading? Vents? (It's open to the air now, though.)