In all honesty, there is not one sure-fire solution. Results will vary greatly from yard to yard and may even differ from year to year in the same yard. Experimentation and persistence will ultimately give you the best success.
1. The first defense is prevention and barricades. You can accomplish this by installing wire screen 2′ below and 6″above all around the proposed planting area. This can take some work but that is what they rent trenchers for.
2. In our stores, we carry a product from Bonide called MoleMax. It’s active ingredient is Castor Oil, and it is an effective means of repelling moles and gophers that can be safely used around children, pets and plant life. In it’s granular form, you just sprinkle it around most of the yard (focusing on active areas) and water it in just a bit. This will hopefully urge the gophers to move out of the yard. It also comes in a liquid form that hooks up to your hose. You can use smaller sprayings, say 1/4,1/4,1/4 etc to direct the animals to the point where you want them to exit your yard. Fish emulsion has also been used.
3. Trapping to reduce the population is advised. This is especially effective in spring and fall. If you use Havahart traps, it is recommended that you bait with a mixture of peanut butter and molasses spread on wheat bread. Check and reset traps frequently.
4. Poison baits are available but recovery is difficult and secondary poisonings of pets or owls is possible.
5. Gas bombs have also been used but usually only after complete rage has set in.
6. Vibration devices also have some success. We carry a product called Sonic Mole & Gopher Chaser. This is a vibrating wand that you insert into the ground and the vibrations drive the gophers out. It vibrates on and off every minute or so. In clay-like soils, one per yard is enough, however, in sandy soils I recommend two. In addition to this battery operated one, there is also a new solar powered version that should work just as well.
Sloat Garden Center sells all the listed devices except the traps and screen.
Keep in mind that gophers are crafty and they adapt to many of the things we do to try to get rid of them. It requires patience and sometimes a variety of “cures” to get them to go away.