My dogs wear a martingale collar with their harnesses. I snap the leash onto the ring for the martingale and the harness (I use front clip harnesses) - that way if they ever happen to slip the harness, they are still attached with the no-slip martingale collar.
Jumping into this thread a bit late, but CAN'T WAIT for a semi-local national for me. Auburn is 3 hours north of Portland and I am really looking forward to seeing you all there! I haven't been to a National since Colorado in 2010.