Julie,

One other thing...how often do you train and how do your scenarios vary?
Do you continually work on one thing until the dog "gets it"? Or do you change it up?

I have noticed with some handlers and dogs that the handler works on one thing.

Example:
Dog is doing well on trail but is slow at the start.
Handler sets up short easy trails in order to only concentrate on the presentation of the scent article and getting a good start.

Dog gets bored of the short easy trails or conditioned to the short easy trails and becomes complacent.
Kind of like "Oh great, here we go again".

Working on an issue your dog is having is great, I do it all the time, but I always make sure the training is different if they are doing well in other areas.

With my Bloodhound, the more I train (for me, not the dog) the more he will "mess" with me. He is a seasoned trailer and knows what he is doing. If I work him too much, he gets pissy, almost as if to say "Heeellllooooo, if you don't get it by now Mom, you never will...."

My other dogs do not mind training a lot, they actually love it I think. Always ready and always willing.