Always, always, always check the backyard gates to make certain they're closed.  Even for dogs that I've seen for 3 years and the gate has never been open, still check!  That way Brady whose cute picture I was going to post here but I can't get photobucket.com to work, won't go for a little excursion in the neighbor's yard (and give me heart failure.)  He was totally fine and came right to me, thank goodness!