Exactly. As I said before, a dog holding it's head up during a walk is not natural at all and it will not continue to do it when you slack the lead. That nose will go streight to the ground. The key is training the dog to have self control on walks. The dog can sniff the ground, but must also keep up. So a properly trained dog will not be totally consumed with a scent on the sidewalk. Dogs are not visual creatures, they are creatures of scent. A dog that is allowed to smell will be enjoying the walk much more than a dog who has no other choice but to look ahead.

Be carefull in corrections with a gentle leader- they can snap the neck. It comes with instructions- USE THEM..
If I remember correctly, your not supposed to snap the leash at all with the head halti. The way it works is basically prevents the dog from moving forward and if it tries to lunge or pull, it ends up turned around and facing you. I'm trying to look it up, but apparantly the gentle leader homepage is down.