The Question and Answer section for Fantastic Mr. Fox is a great resource to ask questions, find answers, and discuss the novel.
No, I don't believe the farmers wil discover the tunnel..... unless, of course, Dahl decides to write a sequel and needs them to switch locations. The farmers finding and destroying the tunnel would give Dahl the opening of a whole new story.
The digging animals worked hard to dig the tunnels.
Mr. Fox came up with the idea of digging a tunnel to evade the people who pursuing them.