Gophers can be a vexing garden problem with many different solutions. A range of products exist including traps, poison, sonic deterrents, plant protection cages, etc. One product recently mentioned by a colleague that works as an organic, non lethal deterrent is a caster-oil based mixture that is sprayed in the affected area and is supposed to deter gophers. This is another option to consider when countering these subterranean pests.
One spray called Gopher-Mole Med, is supposed to last for up to two months per application.
Image from Wikipedia