You do not need a return ticket - in fact most
airlines won't book
flights that far in advance (two years? HAH Many airlines have problems with flights more than 8 months in my experience...). You can get what is called an "Open-jaw" ticket - you book a return trip but for a small fee (for students, $50, for everyone else $150) you can change the returning
flight to anytime within a year less one day of your departure. You cannot change the route, however, so if you book a
return flight from London to Toronto, say, you can't change it to a return flight from London to Vancouver.