It is not uncommon for dog owners to end up with some brown spots on their lawn. This occurs when the dog repeatedly urinates in the same area. The dog's urine contains a high nitrogen concentration that kills the grass. If this happens to your lawn, you will want to plant some new grass seed in that area. This can easily be done on a sunny afternoon.
Get out your rake and pull it over the patches of brown grass to remove the dead grass and loosen up the soil beneath.
Sprinkle your grass seed over the soil where your brown patches were.
Rake the patches one more time. This mixes that grass seed in with the soil.
Pat the soil down with a hoe.
Water the newly seeded patches so that the ground is moist, but not soaked. Wait for your new grass to grow.