I usually recommend wearing old leather garden gloves when installing a trap, moles have a keen sense of smell and if they smell person stink on the trap, they wont get caught. We also have 'mole bombs' , they come in a pack of four and disperse sulphur dioxide gas into the tunnels. Their food source is grubs and insects, they wont eat carrion and they arent vegetarians. Castor beans have a reputation but they are also one o fhte most toxic plants in the world, as Al mentioned, its what they make Ricin gas from (Ricinus communis is the scientific name for them). If you cant kill them, contain them, 16 inches of galvanized sheet metal as a barrier from under the house to the rest of the yard would be a formidable blocker I would think.