We had a vole population explosion here this year and I tried just about everything that I found recommended. None of it worked. I did spray the deer repellent form of liquid Plantskydd on the plants they were felling but it didn't bother them in the least. Nor did cayenne pepper. Nor did diluted castor oil (which according to a study I saw does work but only at full strength - since I was actually having to spray directly on annual plants I didn't know if it would damage them so didn't try). The only thing I tried that worked was a "tin cat" trap. Once they go in there for the bait they can't get out. You can get them in hardware stores and farm supply stores around here. They look like this:
https://www.amazon.com/dp/B00004RAMU/
I seemed to be mostly catching young ones, though, I'm wondering if the older ones were too fat from eating the plants to get in! I've caught the bigger ones in the past in Havahart type traps but those also catch chipmunks during the summer. That may not be such a problem in winter when the chipmunks aren't around.
