Remember the hook and eye latches from the old wooden screen doors?
Here;
http://www.lowes.com/pd_58425-37672-...ductId=3058261
They even have some now with a double catch;
http://www.lowes.ca/hooks/the-hillma..._g1373200.html
These are easy to install without having to be too fidgety about lining things up like you might with real hinges.
Three of them at the edges of the shutters will tie them tighter well enough that the wind should not knock them over on you.