I think it's better to have the niggers breed with the wife than the daughters and only after the wife has given birth to white kids from her husband.
White wives should have nigger male concubines that would breed them. If a boy is born, he should breed a nigger bitch or his white mother or his white grandmother if she is still fertile. If a girl is born, the white husband should breed her. If a boy is born from that pairing, he should breed his father's white wife, his grandmother or his sister. If a girl is born, the white husband's son should breed her.
The white daughter should not fuck niggers at all until she marries a white man and gives birth to his children. Then she may take her mother's bulls or some biracial male offspring as her personal nigger breeder.
This will create a two tiered white race, one that is always pure of any nigger genes and one that has a small mixture of nigger genes. Basically, white latinas.