Question
I need your expert advice. I have a vole problem. Holes keep opening, I have done some trapping, no voles for 4 days, I close up the holes and next day another hole. What do you recommend for extermination? I have heard of a poisonous dust to shoot down the hole, but I don't know if it's available for purchase across the counter. Looking forward to your advice. Thanks

Answer
First, make sure you have voles and not something else.
Second, you didn't say how many traps you used or what your bait was.
Trapping is very effective provided you do it right.
As for the dust, you would need a pesticide license.

Visit http://www.icwdm.org/wildlife/voles.asp  scroll to the bottom and read my publication (published by Univ. of Nebraska) on controlling voles. It will give you the basics on vole control. Other pubs are there as well on vole control.