What the nose Knows
A great video that explains a dogs ability to know it's environment through scent. this gives you a better idea of why our dogs seem to ignore us when the nose is engaged. For those of you that have a breed of dog specifically designed for their ability to track or hunt then you will know exactly what I mean when I say "nose on, ears off!"
So rather than getting frustrated and angry, understand it and work with it instead of against it.