Since gophers reside in tunnels underground, injecting poisonous gas into the tunnels is one method of control. Smoke can be injected into the tunnel by using an exhaust hose attached to a gasoline-powered mower. The carbon monoxide that enters the tunnel kills the gophers or forces them to the surface, where you can kill them. Alternatively, highway flares that produce sulfur fumes can be introduced into the tunnel to force the pests out. Be sure to seal all the exit holes, as leakages make the gas less lethal.
Should the idea of killing gophers sound too inhumane, an alternative is to repel them. Some plants are gopher repellants and are used to make commercial sprays. Pepper sprays, for example, are sold as repellants against pests such as moles, squirrels and groundhogs. Jalapeno peppers are especially effective, and planting them where the gophers are invading will drive the pests away. Other products that repel gophers include the garden plant poinsettia and organic garlic oil.
Create the Predator Illusion
Gophers are scared of cats and dogs. The smell of cat litter sends the message to the gophers that there is a predator around, and they flee. The predator illusion can be created by spreading the fur and used litter of the household pets in areas of the garden where gopher activity is evident. Use of pet litter is similar to the use of ammonia, which is one of the products commercially available as a rodent repellant. Pet urine contains ammonia and is an effective gopher repellant.