Is it permissible for a husband to ask his wife to insert objects into his anus, and is this act forbidden?

It is not permissible to insert a finger or anything else into the anus, as this leads to the abomination of sodomy, and due to Allah's saying in the Hadith Qudsi: "O My servants, I have forbidden injustice for Myself and made it forbidden among you, so do not commit injustice against one another." And whoever does that is unjust to himself.

This act also leads to the loss of a man's dignity in the eyes of his wife, and to potential harm that may result from it.