Question
what is causing my grass to spot, my yard was fertiliesed and now where ever my dog pees the grass dies, didn't do it before the fertilizer.

Answer
Dog urine has high concentrations of soluble salts. Too much salts and the water is forced out of the roots i/o flowing into the roots and the grass plants die of thirst (literally). Fertilizer is also salts. You can improve the conditions by watering the lawn really well after applying fertilizer (1-2 hours using a normal sprinkler attached to a garden hose at normal household water pressure). You should also make sure you apply the fertilizer at the recommended dose and that the fertilizer spreader is calibrated correctly. Finally, you can apply fertilizer at half strength more often (but still water deeply after applying) to dilute the salt concentration in the soil.