Mark and Pete's statements regarding being able to reproduce cross-country courses is true for the vast majority of cross-country courses, but not all. John Tucker has developed some ways to archive critical points that are not well defined by landmarks. You're also starting to see schools (usually at the college level) develop permanent, dedicated cross-country courses.
I think it's safe to say that anybody willing to shell out what it might cost to have one of us measure his cross-country course is probably going to document it in a way that he can reproduce it season after season. Either that or it's a meet so important that it is required to be accurately measured.
Add me to the list of those who aren't really keen to pull a steel tape over a 5K course. Many cross-country courses, however, tend to be loop courses, or courses that use course segments more than once, so for a 5000 meter course, you might actually be able to tape significantly less than that.