HALIFAX - It's not uncommon to encounter contrasts of old versus new, bleak versus shiny, defensiveness versus forward-thinking-ness.  That is particularly the case in Halifax, which enjoys a vibrant present as well as a rich and not always happy history.  I was reminded of that on a single day last week. First, I tried to visit the World War II observation posts and gun batteries  at York Redoubt historic park near Fergusons Cove. Besides being a pleasant walk, this is usually a great spot to view the entrance to Halifax harbour -- which is also why antisubmarine nets were stretched from here to McNabs Island 65 or so years ago, protecting the harbour from the U-boats that plied Canada's east coast, torpedoing naval and merchant ships. You can't get to the WWII location now, though.  Parks Canada has cordoned it off because it is sufficiently decayed and unmaintained that it might be a risk to park visitors.