Not everyone likes them, but I remain very partial to the (period-correct) Pletscher "mousetraps." You can protect your stays by putting thick clear vinyl tubing around them where the rack clamps to the frame. The other trick all of us did back in the day, to keep the rack from sliding downward and scarfing the stays, was to flatten an L-shaped reflector mounting bracket in a vise to create a straight strip with a screw hole at each end. We then mounted this on the rear brake mounting bolt and one of the two rack bolts. Pletcher and others made similar fixtures, but the homebrew ones worked well.