Dog urine isn't the only source of brown spots in a lawn. Even on the best-kept turf, patches can appear for no reason at all--or so it seems. In most cases, the only cure is to dig out and replace the grass, but knowing what caused the problem will help you keep the new crop healthy.
Identify the problem. Most come cases are: compacted soil, heat reflectors, human inattention, overwatering, overfeeding, thatch or sloping ground.
For compacted soil, you will have to reroute lawn traffic by creating a foot path or stepping stones. The problem comes from feet beating a trail in the grass, packing soil particles together so that roots can grow sufficiently. Areas with heavy clay soil (that's you Southeast), are particularly susceptible. If the entire lawn suffers, use a core aerator in spring and fall.
For heat-reflector damage should be treated by watering sun-baked areas of the lawn more frequently. This type of damage usually stems from large windows, light-colored walls and paved surfaces reflecting the sun's heat onto nearby grass, quickly drying the blades to a crisp.
Be careful! This is the only way top cure patches that arise from human inattention. They're caused by neglect or ignorance, so keep in mind that leaving a mower running, spilling gasoline, oil or fertilizer, and leaving objects lying on the grass can cause this.
Find out how much nitrogen your grass variety needs, and stay within that limit. Too much high-nitrogen fertilizer (i.e. overfeeding) can burn blades of grass.
Water your grass one to two inches a week (from sprinklers or rain). More than can flood the grass, washing out essential nutrients, leaving the grass weak and vulnerable to pests and disease.
To fight sloping ground, use golf spikes or aerating sandals (available at garden supply stores), and walk across the sloping area to puncture holes in the soil. This is typically caused when the ground is too dry to absorb water, and the water runs off a hillside before it has a chance to sink in. Aerating the soil will offer the water a chance to soak in.
If the grass feels spongy when you step on it, it's probably thatching that's doing it. This is when a layer of dead grass blades build up on the soil surface, blocking the flow of water and nutrients to the roots. Remove thin layers of dead grass with a de-thatching rake (found at garden supply stores). To prevent in the future, top-dress the lawn twice a year with a small layer of compost and light fertilizer.