running away

Question
we got our Aussie/ Border collie mix last November.   She is just a wonderful dog.   BEAUTIFUL!!   The ONLY problem we have with her is that every time we leave (38 acre farm) no fence, she runs the neighborhood.   She has been picked up by Animal Control and there have been times when we just can't find her.   She is SO smart.   Sit, Lay, Shake Hands, Open the Door, Close the Door, Roll Over.   We don't stay on the property at night.   I love this dog and NEED for her to learn to stay here, any suggestions?

Answer
Well, allowing her to run free is NOT the answer.  Dogs don't have any idea where boundary lines are, and why would they?  Everything smells interesting out there in the wide world and they just follow their noses.  Even on a farm, I would never leave a dog loose and just leave.  Instead, provide a safe kennel, stall, or other accomodation where whe will have shade, water, and a place to be.  Also, make sure you teach her a good recall.  Inexpensive DVD by Leslie Nelson, called "Really Reliable Recall" can show you how.  You may get scoffed at by some of your farm neighbors, but you will probably have the best recall of any dog around if you follow the instructions explicitly.  Recall is always taught first ON leash, not off.  After all, if the dog is off leash, how would you hope to enforce "come"?  Chasing the dog only makes them want to play the game more.  
Please reconsider your desire to have her simply decide to stay home.  Not all dogs will, and plenty of good farm dogs end up dead at the side of the road, or in the pound, because their owners thought the dog should be a mind reader about boundaries.   Alone outdoors, she is subject to more hazards than just the Animal Control Officer or cars and trucks.  There must be coyotes or other predators where you live, and if you are in farm country and she wanders on to another farm, she may meet up with a livestock guardian dog that will not be too happy to see her.  If you really love this dog, and I sense that you do, you might want to get some cheap fencing to contain her (www.bestfriendfence.com) or kennel her when you go away from the property.  JMHO, and I have farm dogs, too, although the farm is more of a "farmette" - much smaller acreage.