There are certain combinations and planetary positions which are being presented here to facilitate an easy reference on the matter.
1. Sun & Saturn jointly interfering with 7th house either from Ascendant or from Moon or even in navamsa Chart. The interference can be through occupation of the 7th house, or aspect of these on 7th house or 7th lord. However a strong benefic influence may either render them, wholly ineffective or partially neutralize malefic influence. Thus giving marriage in some odd unconventional ways.
2. Sun and Saturn jointly influencing Venus, the Karka for marriage. This influence is more damaging in the charts of ladies.
3. Ascendant trapped between two malifics e.g. Sun in 2nd and Saturn in 12th. Other way i.e. Sun in 12th and Saturn in 2nd is also pretty bad as this also constitutes what is known as Papakriti Yoga, but malefic influence is high when Saturn is in 12th as in that case it will influence Sun and 2nd house also Other wise also, if the degree rising in Asc. is surrounded by malefics in the same sign even, the effect is adverse.
4. Similarly 7th house trapped or sand-witched between two malefics placed in 6th & 8th houses, may deny. If 7th lord and Venus are also subjected to malefic influence, the denial is strengthened.
5. Saturn aspecting Ascendant or the 7th house and at the same time Sun & Saturn are either in mutual aspect or having exchanged houses.
6. Malefic planets posited in 2nd and 7th house and some retrograde planet either placed in or aspecting these houses.
7. 7th lord placed with Sun and aspected by Saturn, provided Jupiter is not aspecting or any way influencing the combination.
8. Retrograde Saturn, as lord of 11th house placed in 7th house or even in 9th house may deny marriage.
9. In case a question is put to enquire the possibility of marriage and the chart drawn on the basis of the question time, shows Mercury, in 2nd or 4th house either from Ascendant or from Venus, generates a Sanyas/Yoga i.e. no Marriage.
10. Weak Moon in malefic signs in 5th house and malefic planets occupying Ascendant. 7th and 12th houses, may deny marriage. If marriage takes place somehow, it will not favour progeny and spouse suffers.
11. 2nd, 7th & 12th houses affliected by malefics, so also Venus may create this problem
12. If Sun, Moon and Venus (or at least one out of Sun and Moon) are joined or aspected by Saturn or some of these are influenced by Saturn and the other placed in Saturn sign (i.e. Capricorn or Aquarius) or even in navamsa of these signs may deny the marriage