Concentrated Scent: Dog reaction

[Lilie]

I have a fairly confusing question to ask. I'll try to be as clear as possible.

From what I understand:

When training a dog to track you may use scent particles for the dog to follow. The dog's reaction to those particles remains fairly constant. That reaction gives you a basis to work/train on. (I'm speaking clearly on basics.) Adding distractions and/or difficulty as the dog progresses. Still working/training off of the dog's reaction to the track. My dog works quietly, focused and engaged on the track. Always.

My question is what happens or how do you progress when your dog comes to a highly concentrated scent track? Say a fresh track heavy with scent. The best way I could describe it is if the dog seems 'flooded' by the scent. The track stresses the dog in a way that it backs off, barks at the scent, then continues to follow the scent but stopping frequently to repeat the action (backing off, barking) through the entire length of the track (250 yards). The dog doesn't refuse to follow, or even entertain the idea of leaving the track. But it's clear the dog is stressed by the track. Not even eating the treats/rewards provided on the trail. (And the dog is highly food motivated.)

I use positive training methods and encouraged the dog through out the track. But watching the dog stress made me want to stop the work. I would have thought a highly concentrated track would have been easy and more exciting for the dog and it seems although it was very easy for him to follow, it was the first time I've seen him stress (8 months old) when working.

Any advice on how to proceed?