A navigational system is currently being developed at the University of Regina that has the capability of following a predetermined course very accurately. Formulation of this predetermined course then becomes a major concern in farming a field efficiently. The specific problem of formulating efficient courses around obstacles is the topic of this paper. Techniques of modelling obstacles using graph theory are developed which lead to procedures that are useful in establishing an efficient course. The width of the obstacle was found to be an important criterion. If the obstacle was less than four implement widths, the obstacle should be circumvented with each pass; if larger, one side of the obstacle should be processed and then the other. This approach provides potentially measureable improvements in field course efficiency.