By watching adult movies a couple is choosing a quick sexual turn-on rather than opting to work on their relationship. A married couple needs time to communicate and experiment and through a loving relationship learn how to excite one another. A better solution would be to read the Song of Solomon for some good ideas on love making from this passage of scripture.
I would recommend “The Gift of Sex: a Christian Guide to Sexual Fulfillment” by Clifford and Joyce Penner, Word Book, Waco Texas. There are other excellent books like this one that can give innovative ideas to help couples enhance their sexual relationship.
Also, by purchasing or renting such movies, we are contributing to a business that is morally wrong. In most cases, if not all, the sex is between unmarried partners so these movies are promoting fornication and adultery. God is not honored when Christians participate in something where there is no respect for God and the principles of God’s word are rejected in relation to the holy estate of marriage as a divine institution.