Disease transmission requires that the body fluid of an infected person goes into someone else's body. However, cuts, abrasions or micro-lesions of the skin, including the skin of the penis but especially inside the mouth, are always cause for serious concern. For this reason, safer sex practices are recommended when a mouth is going to come into contact with the genitals or the anus, and deep wet kissing should be enjoyed only if you know that neither you nor your partner has active herpes or hepatitis. Every sexual activity that pleases you can be enjoyed more safely. Barrier protection means that a sheet of latex or polyurethane prevents a risky fluid going from one person's body into another.
Most people take barrier protection to mean use of a condom during genital intercourse.
Find a brand that works well for you and your partners, and make sure you are practiced at using it properly. But barrier protection goes beyond genital intercourse. Chemoprophlyaxis means that potentially infected fluid should be exposed to disinfectant. The best sexual disinfectant currently available is nonoxynol although alternatives will probably soon be on the market. Make sure that your condoms have a lubricant containing nonoxynol.