Definition and Description of Dhurudhara yog given classical text Brihat Jataka by Varahamihira.
Definition
If both the 2nd and 12th houses from the Moon are occupied by planets other than the Sun, the yog constituted is called Dhurudhara.
Description
"A person born with Dhurudhara Yog is born with a silver spoon in his mouth, is very rich and possesses conveyances, is liberal and has many servants."
Varahamihira differentiates this yogas based on the planets involved in formation in the last verses dedicated to Sunapha, Anapha and Dhurudhara Yog in his work Brihat Jataka.
Mars"If the yog is brought about by Mars, the person is full of ambitions, bravery and wealth."
Mercury"If by Mercury, he is clever, with good powers of speech and an expert in arts."
Jupiter"If by Jupiter he enjoys wealth and comforts, is religious and has the favor of king."
Venus"If by Venus he is given to sex, is very rich and lives in luxury."
Saturn"If the yog is created by Saturn, he enjoys other's wealth, house, clothes, conveyances, engages in many activites and is the leader of a group of people."
Explanation
Moon is a very important component of a Birth chart along with Lagna / Lagna Lord. Moon represents almost every nurturing factor of life and this is the reason why Moon is also Karaka for mother, as she being the greatest of all nurturing persons in someones life.
And same is the reason why so many lunar yogas are also associated with wealth and status like Chandra Adhi Yog, Gaja Kesari Yog, Chandra Mangala Yog, Mukuta Yog etc. Ancient Jyotisha classics comprises of considerable number and wide variety of lunar yogas is an indications towards importance of Moon in Jyotisha (Vedic astrology). Jyotisha emphasise the interpretation of a Birth chart from Chandra Lagna, or the position of Moon as Lagna, in addition to the Birth Lagna (Ascendent) gives another clue on importance given to Moon.
Moon by nature is a very impressionable planet (having tendency to be easily influenced by any other planet). She has reflective, receptive, impressionable, feminine qualities.
Moon likes the company or support of other planets, in the same way our mind or manas (in sanskrit) clings to different types of securities. To be noted that Moon is also the Karaka for mind. So by the virtue her nature Moon is acted upon by other planets or we can say she absorbs the qualities and energy of planets within her close proximity, like planets which are in 2nd and 12th houses from her.
Rahu Ketu are Chaya Grahas or shadow planets, they themselves act accordingly of their association and position. It is not mentioned specifically in classics, but Moon’s Node Rahu and Ketu are not included in the formation of these yogas.
Dhurudhara Yog is formed when Moon has planets on both the side of her position. This Yog when compared to Sunapha or Anapha, can be extremely positive or even challenging in some cases.
The underlying principle behind this is whenever any planet or any house in Birth chart is hemmed between by planets on both the side, results of that house and planets within are extremely enhanced when said planets are natural benefics exclusively. On the other side if said planets are exclusively malefics, the house and planet hemmed between suffers a major loss. There are mixed results for malefics and benefics on both side.
Due to the fact that, planets will be on both the side from Moon, 2nd and 12th house. She will absorb the qualities of both of them, so results will be more compound in nature.