Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Basically married couples are allowed to enjoy each other’s body as they wish except what is forbidden, i.e. anal sex, or having sex during menses or confinement period.
Though it is permissible, it is advisable to observe the noble, good and general Islamic decencies in enjoying wife.
What is mentioned in the question even though it is permissible but it is contrary to high moral standards. In addition, it might cause one to touch impurity without any necessity and it might lead to swallowing the impurity.
Therefore, we advise your husband not to force you into something that may lead to some prohibitions, and hence you are not obliged to obey him in this matter and you may reject his demand.
Allah knows best.