I don't know the size of your yews, but the only sure way to protect them is to surround them with hardware cloth. Other types of fencing will protect them from deer, but smaller critters such as voles and mice need to be kept away by using fencing with a very small grid. You can find rolls of hardware cloth with 1/4- and 1/8-inch openings in the fencing department of your local hardware store. If your yews are the upright type and quite mature, you can fence the lower portion and then use one of the repellent sprays that are available. However, these sprays have to be reapplied frequently. Some people hang hunks of strong-smelling bar soap on tree limbs, although with limited success. As with anything, deer become used to that smell, too.

The munching of mice and voles doesn't do permanent damage to your lawn. We really don't want you to put out poison unless there is an area where there is absolutely no possibility of birds, dogs, cats, or anything else being able to eat it. You can discourage mice and voles by keeping your grass cut very short as late as possible into the fall. That also will help prevent snow mold. The trails you may see when the snow melts in the spring will disappear once your grass starts to grow. If there are any bare areas, a small amount of grass seed will help fill them in.