The voter-approved Arkansas constitutional amendment that defines marriage as between a man and a woman goes into effect today. Opponents say the law will harm the rights of both heterosexual and homosexual couples, but lead backer Jerry Cox says the law simply firms up existing law that bans gay marriage. Arkansans overwhelmingly approved the amendment November second. The state constitution stipulates that the measure goes into effect 30 days after passage. Ten other states also passed laws that day banning gay marriage.