For those who have trouble tying up an apron at the back why not use one strap that goes from one side of the apron to the other and secures with a strip of velcro.
I just made this pattern for my granddaughter but it could be drawn to a larger scale for an adult. Very easy, very quick and oh so easy to put over the head and secure.
http://sewliberated.typepad.com/sew_...tutorials.html