Besides a vaccine, how else can I prevent diphtheria?

Vaccine only. The only way to prevent diptheria is vaccination. Even prior infection with diptheria doesn't provide protection. Diptheria is a bacterial infection of the nose and throat. It can cause life-threatening throat swelling. It produces a toxin which damages the heart. Treatment includes antibiotic, vaccination, and anti-toxin. This is a serious disease spread by close contact with other people.
No Way. Other than somehow avoiding exposure and/or "luck", the vaccine, which has been proven very, very, very safe, is the only way.Be smart and immunize.