There are so-called leak patches, also called dental dams.
The term comes from the English and means small latex cloths that are placed over the female genitals or the anus, so that no pathogens can get into the mouth when licking.
Conversely, this can also be used if you want to lick the customer's anus (the technical term is tongue anal or rimming). Alternatively, simple cling film can be used as protection. Attention should also be drawn to the so-called female condoms, i.e. condoms for women that you can insert into the vagina and anus, also to increase safety during anal sex. Unfortunately, they are very cumbersome to use and have not been able to establish themselves in the industry.