Answer: The salts in the urine probably rendered the soil inhospitible to the grass so the best solution is to dig a few inches of soil out of the bare spot and replace it with fresh garden soil. Then reseed the area and water it well. Grass should grow in 7-10 days. It sounds like a lot of work, but you're lucky it is only a single spot and not several spots all over your yard.
Best wishes with your lawn!
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