A vasectomy is the safest birth control method to avoid pregnancy. When the vasa deferentia are cut, sperms cannot make it to the exterior, and therefore there's no way for them to be present in the semen. This surgical procedure is very simple and the accuracy is 99%.
On the other hand, vasectomies don't protect against sexually transmitted diseases (STDs). Men without a steady partner should continue using condoms when engaging into sexual intercourse.