They should get a mongoose. Honestly. A king cobra wouldn’t dare visit a place where a mongoose lives.
Actually a mongoose would flee from a King Cobra. The Hamadryad (KC) is the world's longest venomous snake, with the longest individuals reaching just under 18 feet. Adults are over 11-12 feet on average, and pack enough venom to kill an Elephant. They are also very territorial.
The mongoose is quite good at killing snakes (as well as eating eggs, snacking on insects, etc ....although eating termites is not as sexy as killing a venomous snake). Most pictures one sees of a mongoose involve it fighting an Indian cobra (the Naja Naja is a much smaller species of cobra), and that does occur every now and then (and based on what I have read there is some arms race going on between snakes and mongooses ....whereby the mongoose has some level of immunity to some snake venoms, and snake venoms progressively become more effective against mongooses, leading to a situation whereby one has an upper hand depending on the time).
Anyways, the fact is that a mongoose will never face off against an adult King Cobra (or for that matter even a juvenile). The cobra species that the mongoose would face (in India) is the Indian cobra, although even that is rare. There are far smaller snakes that are not venomous available, as well as a host of insects and earthworms and the like.
The mongoose would always lose against a hamadryad.