sorry to hear your vole woes. I use live traps here, baited with really cheap peanut butter, but I do check them regularly as I hate the idea of them dying slowly in the trap. That being said, I do dispatch them as soon as found (swimming lessons in the cage - they fail). I used to carry the critters abut 10 minutes to the bush and release but discovered (paint tagged them in the trap) that they ran home
In the summer my husband gathers the full live traps and drives them about 10 minutes away for release