Here's a couple of links to the halti. One is a pic of how it looks on a dog and the other is what the package looks like.
http://www.drsfostersmith.com/produc...cfm?pCatId=875
http://www.petsmart.com/product/inde...gkw=halti&sr=1

There is another one out called a "Gentle Leader" but I don't like it as much as the Halti.

They work much like a horse bridle(?) works, by controlling the head of the dog so that he won't pull. If the dog pulls with a halti, his head gets pulled around to the side, then they stop pulling. The halti's are great too in that the part that goes around the mouth will close as it is pulled, pulling the mouth shut. Which I have found very useful especially with my lab that likes to investigate trash that he finds on the road. I just pull slightly on the leash and his mouth closes so that he can't pick it up and possibly eat it....YUCK!!!