A square piece of property has sides each of length one. The
goal is to build a fence on the property such that no two
points outside the property define a (straight) line segment
that runs through the property without being blocked by the
fence. The fence need not be continuous and can be anywhere
on the property. What is the minimum length of fence needed?
Notes:
1. Putting a fence on any three sides will block all lines,
but is not a minimum length solution.
2. There is no 'play on words' trick to this problem.
(Puzzle introduced to me by Ajit Thyagarajan - April 2010)