An obstacle that can cause a great deal of difficulty for agility dogs is the teeter. If you think about it, it makes absolutely no sense to run up a board that slams to the ground when you reach the top. Any smart dog would have to wonder why he should do such a ridiculous thing.
Having a solid, reliable 2 on / 2 off contact behavior on the dogwalk is a great advantage in agility. The 2 on / 2 off is a clear, specific position that most dogs find easy to learn and perform. It also requires the dog to wait until you catch up and release him, which allows for better handling of subsequent sequences. My method for training this behavior involves early foundation skills, clicking for correct position, feeding in position, and back-chaining.
Scent discrimination is one of the "advanced" obedience exercises, but it is actually one of the easiest to train. Why? You are working with the dog's single most acute sense: smell. Although the word is politically charged, in behavioral terms "discrimination" simply means a choice made on the basis of established criteria. In the case of scent articles, that criterion is the handler's scent ("find the one that smells like me").