Yellowing could be from over or underwatering or perhaps a nutrient deficiency or pests. If you think it might be from dog urine, you could saturate the area to try to push that lower in the soil. 

Here is some information on growing irises that has some general care: https://extension.usu.edu/yardandgarden/research/growing-iris

Many of our plant problems are related to water, so I would check to make sure that the soil in the area is moist, but not totally soaked.