Defeating the true Scotsman

It seems to me that there are four ways of beating the True Scotsman self-sealing argument. This fallacy is notable for being impervious to counterexamples; once one is given, one of its components is redefined by the other party to hold his ground. Still, this gives us enough of a foothold to pry a way in.

Symbolically the Scotsman's argument can be presented as:

~∃x(Sx˄Cx)

Read as "There is no Scotsman who does a Crime like that" or  alternatively "All Scotsmen refrain from committing such crimes".  Let's stick with the first reading. Once a counterexample is offered the patriotic Scotsman might reject it by redefining Cx (The chap is a Scotsman but what he did is no crime) or Sx (That's a crime all right but he is not a True Scotsman).

Overall, informal fallacies are best dealt with by bring them out to the open and exposing them by explaining why they are so. A first way then to beat the true Scotsman is to highlight that the argument at hand is a known fallacy and then offering Flew's prime example. This should suffice for most cases, since addressing the self-sealing argument by name shines light squarely on it and the absurdity of its general form adds close to decisive weight to your side.

One can go further in, for the sake of exposition, or to win over the skeptics,  by  directing  attention to the change of definition on which the fallacy hinges to a wider or narrower scope which in any case is different from the intended common use.

Secondly, we can can highlight that no counterexample is possible under the self-sealing strategy which makes the argument a no-go. Whatever is thrown at it can be conveniently redefined away.

Thirdly, this can be further clarified by offering a patently True assertion such as  "There are no triangular circles"  and showing that it even that could allow a counterexample by drawing a figure, showing how to reproduce it or writing down the appropriate equations, while the self-sealing argument offers no such courtesy. Furthermore, one can ask the patriotic Scotsman to offer a counterexample of his own and watch him squirm (though I think this one can backfire as one is more likely to receive a blank stare in return).

Lastly, the best defense is to settle & agree on the definitions before embarking on any discussion. This is especially true when dealing with a known or suspected weasel. One can still act midway by asking what he means by this or that term: "What do you mean by Scotsman?" Ask him to be thorough. Once he or she commits he or she  cannot go back without losing face. Of course it helps having impartial witnesses that can attest to the facts or the ridiculousness of the explanations resorted to by the Scotsman.

More examples of self-sealing arguments that follow the same general form can be found in Critical Thinking: Consider the Verdict (4th) by Waller