I had the opportunity to visit Fossil Rim Wildlife Park south of Dallas Fort Worth recently (a separate review coming soon) and was shooting out of my driver's window. I was so focused on what was in front of me, that I neglected to notice the interloper behind me - until he already had my lunch in his mouth!
Now, from a serious point of view - do make sure you "look behind you" when on nature and landscape shoots. Some of the best shots I've gotten were 180 degrees opposite of my primary subject that day. For example, the light in a sunrise shoot can be just as dramatic on the landscape behind you as the sunrise itself.
Use your eyes as well as your lens when out in the field. Constantly scan the field around you and keep your eyes sharp for interesting shadows and lighting - not to mention the occasional critter!
Stay in Focus,