I have read that you can use large sheets of cardboard covered with several inches of compost, topsoil, or mulch to kill large areas of weeds or grass. One thing they all say is to cover any cracks or folds in the cardboard with extra small pieces of cardboard. You need a lot and need to hoard the cardboard for awhile before trying it. The cardboard will break down over the course of a growing season, but supposedly by that time, the weeds and grass underneath will be dead. Of course if you are treating your entire yard, this probably wouldn't be feasible.
I have not done this before but I always wanted to try it.
