I have to agree with everyone here, getting the big V at 18 is kinda stupid, just a rubber and make sure shes on the pill. Yes i know condoms suck the big one, but you really don't want to herpies or other STDs
and you should do a google search for "my vasectomy", I'd post the link but some of the content is a little much for children.
Oh and just about everyone has had a pregnancy scare when they're young... it goes with the territory....
and if all else fails, just follow the Spartan Dance Team from SNL "Sex Can Wait, masturbate".... Though if you're 18 that skit might be a little before your time.