What poisons have you tryed? Zinc phosphide? Zinc phosphide is an excellent small rodenticide. http://en.wikipedia.org/wiki/Zinc_phosphide
My state is faced with severe limitations on useage of rodenticides and moluskicides. We have to be very carefull and make sure no non-target species are not harmed. Zinc phosphide, properly placed, seems to do that quite well. It has virtually no secondary kill and the initial kill is as humane and quick as possible. The vole/mouse will ingest the bait, go into the hole and die quickly. The carcass then becomes an organic fertilizer as the poison, once mixed with the acid in the stomache, escapes as a gas in extremely low volumes.
With an anticoagulant, the vole/mouse will take a lot of time to die. It may go into the hole and then come back out to die where a non-target species like a bird of prey may ingest the rodent. The anticoagulant poison is still active in the rodent for quite some time after ingesting the poison.
Anyway you look at it, the control of rodents will be expensive. Baits are usually well over a dollar a pound and a minimum of 10 pounds to the acre is required for control in a broadcast application. Enough bait has to be applied to insure a lethal dose. Mice/voles will become bait smart if a sublethal dosage is ingested. Usually this is avoided when there is enough bait available to the rodent. If you skimp on application rates to lower the cost, it will come back to bite you.
For the gophers, I know a lot of people locally and in areas that can still grow hay, have had great success using the Verminator.
Moles,.......I have no idea. We just trap them here as that is about the only sure way to know we got blasted buggers. In a landscape situation, there is a mole repelant that works very well. It is basically a dry for of castor oil. It is spread, then watered in. I have used it and it works very well. But in a large scale field application,.............not. I have also heard that moles dont like garlic. Of course most animals that eat hay, dont like it either I would'n think, so....... Other than trapping a mole, the only other option that I have been made aware of is repelants. Poison control of moles on a large scale I have no knowledge about.
I hope you can find some control as I know all too well being the perennial grass business what damage those blasted things can cause both to the yield and the equipment.