di dee, as many dont use a clicker, and are able to scoop prizes in shcutzhund, i would have to disagree that use of words as a marker are confusing for a dog.
Dogs are very smart, incredibly smart. And know my marker word "yes" and the word "ok" and "sit" and so on and so on.
She is now getting faster with her responses. Lights up for a ball. And wont touch her food, sitting there with eye contact, as i mark the behaviour with "yes", and then dives at it, upon hearing her release word "ok".
I know that she understands "yes" as 'that's right, keep doing what you are doing'. as i can guide her movements now with that word when tracking. When unsure, if i say 'yes' she keeps going. Similarly, both dogs also know the word "no". They will both give up searching on tracks, and change direction if told "no" when heading in wrong direction.
Im sure there are dogs, that need the objective marker method, where no vocal intonation can be misconstrued by the dog. And perhaps for high level bomb detection, scent detection, sniffer dogs etc, where accuracy is paramount, perhaps you need to be stricter. But for me and my pets, "yes" seems to work fine.