Well, first of all, I'll assume you want to keep your dog. That being decided, if there are spots in your lawn from where your dog does his duty, there is no magic way to prevent or fix the problem.
Pets & Your Lawn
Common Sense Guide to Lawn Care & Pet Safety
Pets are like one of the family, and their health and safety are considered along with that of our own children. “Pets and Your Lawn” gives you common-sense advice and safety measures to follow when using lawn care products and services.
Caring for your lawn and following proper turf management practices are essential to a healthy lawn. You and your family can enjoy leisure activities on the thick, cushioned play surface, realize increased property values and, more important, create a better environment for your efforts.