I love this person's coupler/triplers:
3 DOG COUPLER LEASH 3/8"X 5' NYLON SWIVEL SNAP EACH END - eBay (item 130397765478 end time May-29-11 21:48:22 PDT)
See how there is swiveling action at both the top and bottom (at the upper main swivel, the upper clip swivel, and the lower clip swivel)? That really helps w/ tangling rather than if there was only one spot of swiveling.