Found this out a long time ago by accident. Ever notice how the best grass seems to grow in the places you don’t want it? Try this method in lieu of chemicals.
Simply take a dark colored tarp, lay it out and the ground where you want to kill the weeds/grass and hold it down with rocks. About a 2 weeks later everything under it will be dead and gone.
Stuff will eventually grow back but it kills things longer and better than any chemical weed killer I ever tried, is pet safe and is obviously re-usable.
Here’s a picture of an area I did (lower center) versus an area I used weed killer on (upper center). The difference is after about 2 weeks in the sun with a black tarp all that is left is dirt, where the weed killer leaves dead brown grass and weeds. You can see a little of the black tarp in the foreground. It’s nothing fancy, but it works well. I haven’t tried it yet but I think you can also use 4 mill black poly sheeting as well.