It's interesting, you two have addressed the two most common techniques in "cracking and stacking". It's true that demographic changes can alter efforts at cracking, if the margins are narrow enough, but stacking is rarely so undermined. Stacking is also at least facially, consonant with "majority-minority" districting. It's actually a fairly conflicted process. As noted, the very process of stacking/majority-minority districting can result in diluting minority interests in other Districts.
Have either of you read Charles Blow's book, The Devil You Know? He proposes that blacks move back to the South to improve the chances of minority representation in the Senate (and other offices), since minorities already represent near majorities all over the south.
A well reasoned argument is like a diamond: impervious to corruption and crystal clear - and infinitely rarer.
Here, as elsewhere, people are outraged at what feels like a rigged game -- an economy that won't respond, a democracy that won't listen, and a financial sector that holds all the cards. - Robert Reich