Gophers hate "bad" odors or odors that they are not used to, such as ammonia. The smell of ammonia can send the gophers away from your garden. One of the drawbacks of using store-bought ammonia is that it is also a chemical that can be harmful to the environment. An excellent substitute that you can use is a used kitty litter to fill in the gopher holes. The used kitty litter with the cat's urine produces ammonia naturally, which can produce odorous gas that gophers cannot stand. Place portions of the used kitty litter into the holes. Kittly litter is a naturally decomposing product; therefore, it should not be harmful to your garden. If you are concerned about the smell of urine in your garden, make sure to cover the holes right away with additional potting soil. Of course, you should already own or plan to own a cat if you plan on using this method. You can also ask a neighbor with cats for their used kitty litters.