Question - rig / hood dog

Wind currents are everything when it comes to a dog rigging. Pay attention to your dog & which way he is facing.
With the hounds I have a couple who will rig tracks & I can tell from her strike if they are hot or cold. Now if every dog blows up, they are catching body scent & normally the hog will be within 400 yards.
Just like Jon said, a lot of times dogs can smell hogs from the top of the rig but once they are on the ground they cannot smell it. Experience will teach them & also teach you to read your dogs.
I have had dogs strike hard & go almost 600 yards to the hog itself & bay it in it's bed.
A good rig dog sure can make it a lot easier.