The easiest way to enforce this is enforced chastity.  The longer he is chastity the more agreeable something like this becomes.  This is great training.  One of the things you want to do to train your husband to be more compliant and obedient is to shift his focus from his cock to his ass. Once you have trained him to be excited to get fucked in the ass, you will have a very well trained husband.  Ass plugging him fulltime preps him for this, and stretches his anus so that you can keep on sizing up your strap ons.