What about repentance after anal sex with one's wife? Please advise.

It is in the nature of man to commit sins, and the best among them are those who follow a sin with repentance. Repentance is obligatory for all sins. Allah has opened the door to repentance day and night until the sun rises from the west or a person is on their deathbed. The questioner should sincerely repent to Allah, and frequently seek forgiveness and perform good deeds.