I have voles in my lawn (midwest) What is the recipe for using castor oil to repel them?

Castor Oil For Voles

Voles are terrible little animals, but... If you aren't trying to grow food.... Probably should just ignore them.
YouTube is full of videos for trapping them... But they reproduce so fast that even a herd of cats doesn't seem to appreciably affect the vole damage at my house...
I've purchased vole repellant, which mentioned castor oil as the active ingredient... It didn't seem to make any difference.
I've put castor bean seeds in the vole tunnels, and the results were better than using the repellant.
If you were determined to use the castor oil.... Might need to experiment with what will blend with it... Not sure what would happen if tou tried to mix it with water... But... Oil and water usually don't mix... And... Most Stuff that will mix with oil would kill the grass...
I found this recipe... Blend with dish soap...
http://homeguides.sfgate.com/recipe-mole-repellent-gardens-50930.html

Voles or Moles?

That'll not only make the lawn impossible to walk on, it'll likely kill the grass.