Check table list view to make sure value isnt chosen yet - then do not allow the new entry

[Tiger1]

I have a table. Inside the table i have a full list of possible values to choose from. After the user chooses from the list - i want that value:

Taken out of the list
Not to be an option in the table anymore (so there is NO chance of adding the same field twice)

Do i write this expression in the Behavior -->> Action?
Or do i write it in the data set "formula?

Any thoughts?