Trouble

When I first brought Bella home she was a little fluff ball that I kept in the hay shed and took her out for supervised visits with the sheep.  As she grew and the weather warmed up I built her a run by fencing off the front of a three sided shelter.  When no one was home to supervise her she was locked in her run.  Eventually she became large enough that I would only put her in jail (her run) during the night.  

This was to ensure she learned good habits.  The last month I've had my hands full trying to keep her in her run at night.  She has started to break out and while I understand she does this to be closer to the stock and to chase coyotes it has me slightly worried.  Lately Bella has taken to going down to the road.  This is not good.  The road I live on is a busy through fare being the last north south road before a large National Park.  She has been caught jumping up at passing trucks (always trucks) and I do think she's trying to guard, but most Guardian Dog fatalities are car collisions.  

If I catch her heading past the house I give her the standard "Get back to your sheep!" but it being winter and she being white I sometimes don't see her head that direction.  I haven't been able to think of a solution to prevent this bad behavior from becoming a habit.  This weekend I'll be going to town to buy a dog run.  I plan to put the dog run in one of the corrals and lock her in it during the night.  This will be a short term solution.  And I need some long term answers.