We all have the smart guys who lawyer up when asked to perform any field sobreity tasks. Others just plain refuse.
One thing that usually works for me is to say to them after they refuse: “Sir, is there any good reason, other than your state of intoxication, that you are refusing to do these tasks?”
At least two thirds of the time you will get the answer, “Nope,” or my favorite, “No, that’s the only reason.”
This looks great on tape!