Fence in your plants. Use small fencing, such as chicken wire or garden fence, to create a barrier around your trees and bushes. Make the fence tall enough that your dog can't jump over it.
Fence in your dog. Create a fenced-in area in your yard for your dog to keep it out of off-limits areas. Use wood, metal or iron fencing and be sure your dog can't jump over it to escape. Give it plenty of room to run inside of this area, and provide shade and water.
Bury bricks. If your dog digs under the barriers you have set up for it, bury bricks in the places where it digs. The dog won't like feeling of hitting the bricks with its paws, so it will stop digging.
Plant trees and shrubs in raised garden beds to keep small dogs out.
Sprinkle cayenne pepper around plants you want to keep your dog away from. The smell will be offensive when it sniffs, so it will move on.
Wrap trees in wire cloth, also called hardware cloth. Dogs can't chew through it and won't be able to disturb the trees.
Sprinkle the ground around your trees and bushes with pine cones and decorative rocks. Your dog won't like the feeling of these items beneath its feet, so it will go elsewhere.