I have several spots on my lawn where weeds and moss have taken over. I was thinking about spraying those spots with salt water so it will eventually leave a neat circle of sand, once the grass and weeds have died. But I don't want to do this if the salt water spreads out and leaves an undefined shape, instead of the shape I sprayed.

Plus, how long will it take for grass and "regular weeds" to be gone with salt water?

Thanks in advance for your advice!