On the farm we were often plagued with mice. It seemed they were everywhere , and they always found our old wooden barn to be particularly inviting. They also loved our potato patch, and often dug into the hills and dined on the tender tubers. I can remember many years when we had to grade-out hundreds of pounds of tubers thanks to mouse damage.
Mice (and their close relatives voles) can also cause severe damage to young trees and shrubs. Tender fruit trees like apples and plums are a favourite food for these rodents. Trees that become "girdled" by rodents invariably die and must be replaced with new transplants.
So what does one do to control these critters? Essentially, there are three control strategies: exclusion, repellents and traps/rodenticides.
Exclusion should always be at the top of the list. Providing solid physical barriers is the most important first step. Tough, plastic tree wraps provide excellent protection, and well-sealed homes will keep rodents from coming indoors. Just remember that exclusion always goes hand in hand with cleaning up the yard and removing places for rodents to inhabit and hide.

Repellents can be reasonably effective against mice and voles but are not designed to eliminate rodents from your property. Rodents are surprisingly smart and highly adaptive and while some repellents have some short-term affect they often provide poor protection unless applied regularly. Sometimes blood meal fertilizer is recommended as a rodent repellent but I have never found that it works. However, blood containing products like "Plantskydd" are fairly effect for repelling deer and elk.

One important thing to keep in mind that repellents come under Canada’s Pest Control Products Act. What that means, among other things, is that if a product is not labeled as a repellent with a "PCP" number on the label it cannot be sold as such. Thus, a product like blood meal is labeled for sale only as a fertilizer but not as a repellent. 
Rodenticides are another tool for rodent control. Today’s best mouse killers are superior to the old "toss and scatter" baits and, instead, are secured in bait stations. Typically, a bait station includes a solid block of rodenticide that is sealed in a plastic container that has a clear plastic lid and, for safety’s sake, the bait can only be accessed via a mouse-sized entry hole.  One feeding is all it takes to kill small rodents.
Still, there are a couple of other strategies that can be employed if the above three don’t appeal to you. Some people prefer to employ a feline or two to keep rodents in checkwhile others simply shrug their shoulders and tolerate some rodent damage by adopting a "live and let live" philosophy.
As always, the choice is yours.

~Jim Hole