Experts and BHG readers answer.
grass under fenceline
I wouldn't recommend using salt to kill grass. Yes, if you put enough on, it will probably kill the grass. But if you put enough mulch, gravel, etc., that will kill the grass too.
There are many products -- and some good new organic ones -- that will kill the grass. But you'll have to cover the area with something like a thick mulch or the surrounding grass will grow back into the now bare ground.