The theory is that the rodent can 't hear its prey with all the background noise, so it leaves the area. Hard to do with voles. In any case, reduced grubs mean a healthier lawn. In research at the university of Michigan, castor oil has been shown to reduce mole populations. As in the above example, the seed acts as a stomach poison when inserted into the mole tunnels - advised by an 1800's gardening magazine.
Reports are mixed.
Weatherproof mouse bait. Slice the tunnel open, insert the mouse bait chunk and reclose the tunnel. This is particularly effective. With the bait below the ground, pets and children can't get at it. They like the taste - doesn't hurt them at all.