Classical conditioning has nothing to do with behavior and is all about emotion and physiology.
If you remember Pavlov’s dogs, you remember the bell, food and drool, but nobody knows what the dogs were doing while the bell was being rung and the food was being presented. That is because the dogs’ behavior was not part of the experiment. The experiment was about physiology, making the dogs drool was the point.
Classical Conditioning can and should be used to alter or reinforce a state of being, location, or physiological response to a situation.
Markers are not necessary and are counter-productive when working classically to adjust your dog’s state of being, emotional state, or physiology.