Rodent damage to the trunk at the soil line happens when grass grows tall next to the trunk. Remove the grass and weeds using hand clippers, not the string trimmer, as that can cause more problems. Rodents love to hide in the grass, and they will happily eat the bark off the trunk and the surface of the roots. This feeding can girdle the tree, causing it to die.
Rabbits love to eat thin barked fruit trees (and other thin barked ornamentals), as well as any young tender branches and twigs within reach while standing on their hind legs. Once trees develop the heavier, thicker bark, rabbits seem to leave those tree trunks alone. However, they will continue to eat those tender branches. Mechanical barriers are the most effective method of preventing rabbit damage. Use a cylinder of chicken wire, hardware cloth or fencing specific to keeping rabbits out which has graduated openings. The openings are narrow at the bottom and get bigger the higher up on the fence. Young rabbits will not be able to get inside in the spring either. You must secure the cylinder of wire so the rabbits cannot push it over and feed, and it must be higher than any expected snow or snowdrift common in your yard. Since fruit trees are often branched low to the ground, a wide wire cylinder is often the most practical. A larger diameter and taller wire column is needed if you also have deer feeding on a regular basis.
There are other materials, such as spiral plastic wraps or commercial tree wraps, that are applied once cold weather is here to stay. The best wraps will be lighter in color to reflect heat away from the trunks. Wrapping the trunk also will have additional benefits, preventing winter sunscald and frost cracks. When the trees are wrapped, we are not trying to keep the trunk warm, but rather to shade the trunk from direct sunlight that can raise the trunk temperature above 32 degrees and cause that freeze crack. These cracks are most common on the southern or western exposures of the tree trunk. This damage will not show up until the following growing season. Remove the wraps after any chance of frosts and freezing temperatures in the spring. This allows the trunks to grow in girth and develop hardier bark.
One area often overlooked is water drainage away from the trunk at the soil line. Fruit tree trunks standing in water and then being frozen causes damage to the trunk, leading to crown and root rots. Be sure to allow for drainage away from the base of the tree for the winter.