Ive been carrying Kryptonite on the racktop for about 30years and it hasn't broken so far.
I stretch a bungee chord across the top of the rack, either a long one from the lower hook of the rack, or a short one wrapped around the top. The shackle is placed under the bungee with the loop wedged under the front stop of the rack. There is no rattle, the rack is available in an instant, no toeclip to mess with. In a defensive scenario, I can grab the shackle and go to work. The pannier fitting (Klickfix or Ortleib) works with a looped bungee chord with no interference. I do have to remove the lock to fit the pannier but the bike is often locked up at that point.