Is it permissible for a husband to fondle his wife's anus without penetration, and is it permissible for a woman to do the same?

The basic principle is that each spouse is permitted to enjoy the other's body, except for what the Shariah has forbidden. It is permissible to fondle the wife's anus without penetration, but it is better to avoid this to prevent falling into the forbidden act of anal intercourse. A wife fondling her husband's anus is an abhorrent act, contrary to both Shariah and human nature.