Round patches on the lawn about 100mm wide with dead grass in the middle and dark green at the edges are called dog spots.
The patches occur when a dog wees in the same area a number of times and the high concentration of acids, salts and nitrogen in the urine burns the grass roots.
Dig out the dead spots and replant the affected area by adding topsoil and grass seed to match the surrounding area.
Prevent spots by giving the dog plenty of water to make its urine less concentrated and soak its favourite areas of lawn to flush salts out of the root zone before they kill the grass.
Train the pet to urinate in a special spot and cover the area with mulch.
Sprinkle topsoil in a thin layer then add an even amount of grass seed, covering with another thin layer of soil. Keep the area moist until the new grass is about 50mm high