Logs are used for Retaining Walls , Garden Edging or fence posts All Treated Pine logs are suitable for in ground use H4 products are for in-ground or ground contact use outdoors. Typical use of H4 products include, fence posts, sleepers, landscaping, garden edges and garden boxes. Resistant to rot and attack by termites or borers. What does an H3, H4 and H5 Rating Mean? - The H rating for Treated Pine is an indication of the use to which the timber can be put and its resistance to rot and attack by termites or borers.