To your dog, Sit and Tatonka are the same. Use the command after the action

I think it's pretty safe to say everyone recalls the scene from Dances with Wolves when Kevin Kostner's character is trying to communicate with the Native Americans about buffalo.  If you don't, here's the video :-)

Teaching a dog a new command should be communicated in a very similar way - the action must precede the word.  I'm not suggesting you get down on all fours to demonstrate something for your dog, but what I am advising is that you wait until your dog completes the desired action before you try word association.  Once they perform the action, feel free to start associating any word you like.  "Sit" can be "Tatonka" in your house if you prefer.

Let's use "Sit" as an example.  If you continue to say the word "sit" while your dog is standing, he will simply learn that "sit" means to stand.  BUT if you wait until your dog sits of his own choosing (or you can encourage him to sit by using a treat to shift his weight backward until he has to sit to keep his balance) then you are teaching your dog that the word "sit" means to sit.

Another analogy to consider is: If you encounter someone who does not speak English and you want that person to learn the word for "nose," would it be better to:
a) say "nose" when the person points to her nose and "eye" when she points to her eye?
b) keep saying "nose" even if the other person is pointing to her eye in hopes that eventually she'll point to her nose and you can give her a treat for finally figuring it out?

I hope you chose "a". :-)  If you want to teach your dog a command associated with a particular word, then be sure they can perform the command BEFORE you associate the word or else you'll just confuse your dog and frustrate yourself.