Traps help. Plants don't. Both the scissors trap and the cinch trap have staunch advocates.

do gophers make underground tunnel runs or do they just dig a burrow?
could you have moles instead of gophers?
the plant ricinus communis is called the castor bean or mole bean plant and is said to kill moles which might eat a bean that you might drop into its hole. ;-)
the seeds(beans) contain ricin, a poison when ingested.
i think the traps would be your best bet, though.