How can I achieve a durable finish by using polyurethane over linseed oil?

To achieve a durable finish by using polyurethane over linseed oil, first apply a coat of linseed oil to the surface and allow it to fully dry. Then, apply multiple coats of polyurethane, allowing each coat to dry completely before applying the next one. The polyurethane will provide a protective layer over the linseed oil, enhancing durability and longevity of the finish.