I am about to build some basement shelving out of untreated 2x4 lumber and I'm wondering if there are any alternatives besides using treated lumber to protect the butt ends of the legs from contact with the bare concrete floor. I've seen a few options for leveling feet but they seem to rely on being screwed into the side of the leg which would seem to compromise the load bearing capacity of the shelves. What's the best way to tackle this problem?