It seems that the regular old kind of "married" that most people get wasn't quite married
enough for the Huckabees:
"The Huckabees married in 1974. They entered into a covenant marriage in February 2005."
From Wiki (emphasis mine):
In the United States, a covenant marriage is a modern concept of marriage considered to be a cultural and political response to no-fault divorce. Couples in a covenant marriage agree to obtain pre-marital counseling before marrying, and accept more limited grounds for divorce.
Legal covenant marriages are currently available as an option in Arkansas, Arizona, and Louisiana, which became the first state to approve them in 1997. People who are already married in these states may change (or "upgrade") their marriage to a covenant marriage.
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It is more difficult for couples who have a legal covenant marriage to obtain a divorce; cause for divorce is typically limited to abuse, a felony with jail time, or adultery. To date, the number of couples choosing covenant marriage in the states that have adopted it have ranged between 1 and 3 percent of all marriages.
Opponents of covenant marriages argue that they are too religious in nature, effectively legalizing a religious view of marriage. Some worry that women can become trapped in unhealthy marriages - even in cases of abuse, it can be difficult to prove allegations sufficiently for a judge to grant a divorce. However, it is currently still possible to file for divorce in a state that does not recognize covenant marriages.