God places no limitations on what happens in the marriage bedroom.
"Marriage is honourable in all, and the bed undefiled" Hebrews 13:4
So, according to the Bible, anything goes!
Stan, I'm sorry, but you are taking this verse way out of context, and teaching a falsehood.
Starting from the previous Chapter:
1 Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us, 2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God... 14 Follow peace with all men, and holiness, without which no man shall see the Lord: 15 Looking diligently lest any man fail of the grace of God; lest any root of bitterness springing up trouble you, and thereby many be defiled; 16 Lest there be any fornicator, or profane person, as Esau, who for one morsel of meat sold his birthright... 28 we receiving a kingdom which cannot be moved therefore, let us have grace, whereby we may serve God acceptably with reverence and godly fear: 29 For our God is a consuming fire. 1 Let brotherly love continue. 2 Be not forgetful to entertain strangers: for thereby some have entertained angels unawares. 3 Remember them that are in bonds, as bound with them; and them which suffer adversity, as being yourselves also in the body. 4 Marriage is honorable in all, and the bed undefiled: but whoremongers and adulterers God will judge. (Hebrews 12:1-2, 14-16, 28-29, 13:1-4)
The context is walking in the fear of God, who avenges sins, and brings punishment upon adulterers and whoremongers. Now, the translation "Marriage is honorable in all" needs to be changed in light of the way it is often being taken by many these days, because it gives rise to a complete misunderstanding of the passage. The word "in" can just as easily be translated as "among," and this would save things from being misinterpreted by some to their own hurt. The context tells you what is being said. "Brotherly love" in verse 1 refers specifically to showing Christian hospitality to the unfortunate, the widow, the orphan and the stranger, as confirmed by verse 2. Verse 3 is about likewise giving shelter and/or protection to those who suffer adversities for Christ's sake. Verse 4, then, is a warning about the dangers of adultery being committed when hospitality is shown, such as when someone stays too long, makes themselves too welcome, and a sin is eventually committed against one who showed hospitality in good faith. Thus, the words "Marriage is honorable amongst all and the bed undefiled, but whoremongers and adulterers God will judge," is simply reinforcing the teaching that sexual relations are permitted to married couples but not anyone outside a marriage relationship, and especially not against someone showing hospitality. It is NOT therefore saying, "Any sexual act committed between two consenting married people is acceptable before God." That is entirely out of context. It did not matter under Old Testament law if the husband consented to his wife committing adultery. She would have been committing the sin regardless, and would have still been subject to judgment under OT law. Likewise, God was still executing judgments under most such circumstances during New Testament times (the woman caught in adultery being an exception to the rule). But as the above passage - among
several in the NT - points out, it was being avenged during New Testament times. Thus, the command was to walk in
holiness and the fear of God.
As for sexual acts that constitute sodomy, do these fall under "walking in holiness or the fear of God"? No. Scripture also declares, "Mortify therefore your members which are upon the earth; fornication, uncleanness, passion, wicked lust, and covetousness, which is idolatry" (Colossians 3:5). The "covetousness" referred to here was sexual covetousness, just as in the OT, where they were commanded not to covet their neighbor's wife, and the term "idolatry" could be taken is referring to this covetousness or to the entire list. Even in our moral corruption today, what would most describe it as if there was a holy sister who walked continually in prayer and was clothed in the Holy Spirit and walked in great spiritual gifts, and the man who married her subjected her to anal sex? It would be an unclean thing. It would constitute what the above passage calls "wicked lust." The problem is, we don't walk in anything resembling holiness these days, so we don't even recognize what it would look like in the marriage bed. Moreover, we're often simply "having sex" rather than making love, and this leads to sin as well.
As for the ones who say missionary position only, that is just ridiculous. Love making can take many positions, and so long as the focus is on romanticism and not "performing," it is acceptable before God. But demons do and will tempt Christians to engage in all forms of uncleanness, and to promote actions which like adultery do indeed defile the marriage bed is to do others a great disservice before God.