I’m afraid there isn’t much you can do to repair the damage once it’s done. Given enough time, any dead spot in the lawn will fill in eventually. Your dog’s urine is acidic. Female dog urine is more acidic than males. Of course the bigger, and more energetic your dog is, the more water it will drink and the more it will urinate. The urine, being acidic, changes the pH of the soil. Grass requires a pH of 5.5 to 6.5 to thrive. The more acidic the soil, the greener the lawn. You’ve probably noticed that around the very edge of the dead patches that the grass is usually darker green. This dark ring of grass around the dead spot is growing in acid soil that has improved the colour but isn’t acid enough to kill it. Whenever the pH of the soil becomes too acidic, or too alkaline, the grass cannot survive. Over time, and with the addition of sufficient water, the pH of the soil will rebalance itself, and the lawn will try to fill in the bare patches. The key to avoiding these dead patches is to try and prevent them. The easiest way to do this is to keep your garden hose handy. When you let your dog out, watch where it goes and immediately water down the area to dilute the acid. This will likely prevent the formation of any distinct dead patches, although the overall colour of your lawn may still appear a little spotty.