I own a very loving male English Setter. In the field and around the house he will try(mostly succeed) in doing what I ask. He is happy, confident, gentle and mild manner dog. Daily(most days twice) I take him to a field and release him from his leash(he's very good at following directions off lead). This is by far and away the highlight of his day. I need to take him on lead to the field through a highly urban area and he pulls excessively - he is in a hurry to get there and extremely focused on the matter. Treats, praise etc will not break his focus(it's as if they don't exist). He's strong(my wife can't walk him due to this) and it makes it drudgery to take him. I've trained other dogs through obedience school, but this one wearing me down. What do you suggest?