Here's a situation many homeowners have faced: You spilled some fertilizer and killed a patch of grass. Then you reseeded the spot, and nothing happened. Finally you laid sod over the bare spot, and the sod died.
Here's the solution: You're up against contaminated soil. And whether the contamination is from fertilizer or doggy doodoo, the solution is simple. First, turn the soil over. Drive a spade deep into the ground and flip clumps of soil over. That buries the most contaminated top layer of soil deep in the ground where the contaminants will dissipate before new roots grow down that far. Then flood the area with a garden hose for at least 15 minutes. The water will drive contaminants deeper into the soil. Now you're ready for seed or sod. Be sure to water the new grass daily until it's established.