I always walk Bear and Jas on seperate 4' leads with a prong collar, one dog on each side of me.
http://www.rottweiler.net/rottie/smile.gif They have both been taught the "by me" command, which makes walks much more pleasant...
http://www.rottweiler.net/rottie/smile.gif Like anything, walking two dogs at a time takes time to practice and get used to.
I agree, the coupler can cause more problems than it is worth and as Judi pointed out, both dogs would recieve any correction you give.