You enjoy your arborvitae tree, but unfortunately, so do many pests and animals. Arborvitae is delicious to animals and it is difficult, though not impossible, to keep them away.
Deer, moose and rabbits are the most common eaters of arborvitae plants. You can try to keep them away by putting an animal repellent on the leaves of your plant that will make the leaves bitter, however, this method usually will only work for a while until the repellent wears away.
The best way to prevent animals from eating your tree is with mesh fencing to prevent the animals from getting through.
Though fencing might keep out larger animals it will not protect you from scale insects or aphid attacks. If you are having insect problems, it may be necessary to spray your tree with an organic repellent that will not harm your tree. Also, remove any infected leaves or branches from the tree to prevent the insects from spreading.
If you continue to have problems, consider planting plants that naturally repel insects near your arborvitae. This will help prevent their survival around the area.