How to get a large puppy to stop sniffing/ pulling like a freight train?

I had this same exact problem with my dog and used the harness and stubborn thing still pulled too my next solution was to get a leader. This is like a harness that fits like a muzzle almost. You put it on them attach it to the collar and put their leash on in the middle of the part that connects it to the collar. Basically what this does is it turns his head every time he pulls. He may still try to but he'll stop on his own. When we put this on my dog for the first time it was like walking a whole different dog.