any info on Voles (eat, yard, dry)

[loves2read]

we apparently have a back yard that has a colony of voles (smaller than moles and they eat vegitation not grubs)---my husabnd bought the dry pellet-type of poisoned bait last year and used it and we thought they were gone...now this spring we can tell that our grass is dying because they are eating the roots (below ground) and we are seeing the little mounds of earth that they pooch-up when they come to the surface and when we walk in yard we can feel the tunneling ...

if we call an exterminator will he do anything except put out more bait--I am concerned because we have a dog that we let outside (usually unsupervised) for periods during the day and I don't want her to get into that poison.
I even wondered if we would have to have the whole yard rototilled to expose and chuck them out--it seems that there are going to be big patches of grass where they have eaten the roots which will have to be resodded anyway....

anyone else have a problem with these animals-- or ideas for how to get rid of them...right now they are in back yard and haven't gone to side or front...trying to keep it that way...