The most effective and humane method of ridding a yard of gophers and other similar pests is the use of castor oil granules or similar products. Other methods include setting live or lethal traps, or purging a tunnel with a garden hose.
Castor oil granules do not actually harm gophers, but simply deter them from entering a yard. Water the granules into the ground or spread them over the top layer of the grass. Traps require a gopher to come to a certain area, and therefore require bait and manual removal of the pest. Smoke bombs and poisons are generally less successful methods of fighting gophers.