You can control gophers and ground squirrels by planting chickling vetch (AC Greenfix) around their burrows. The plant, which also works as a green manure, contains a neurotoxin in its tissues which is concentrated in the seeds.
If you plant a field in chickling vetch, the following spring, the rodents will eat around their holes and ingest the plant tissue and also some hard seed that didn’t germinate the year before. That fall, you will find cobwebs around every hole in the field.
—from a conversation with Larry Marshall, Saskatchewan