Most design contracts are supposed to be paid in full when the last hole is seeded.
No course is ever really "done" if you want to stay in touch with the client and make sure it's getting the proper TLC, but once we are finished with construction, it's the client's course, and we participate at their choosing. A couple of architects have "don't touch" clauses in their contracts where they can take their name off the course if they don't like something the client does to it -- usually there is a time limit on that clause, and I don't know of an example where it has been exercised.
Even on the best of courses, there is usually a sense of relief to be done with the project, and I have little desire to go back and tinker around afterward. Pacific Dunes was an exception -- it was kind of a letdown when we were done, and I was pretty sure there wouldn't be much need to go back in the short term.