Dog Pee: Nature's Herbicide

This spring I realized that my dog had been peeing all winter in one spot in my rock garden.  

I knew dog pee wasn't good for plants, but I had no idea it could be so devastating.  Now I've blocked off the area with potted annuals and herbs, and the sedums are starting to spread into the devastated area.  It actually looks ok, and it's handy to have the herbs so close to the back door and the kitchen.  I can't wait to see how the garden looks next spring, after a whole year of protection.

Here's the culprit, looking completely innocent:

 

I thought about trying to train him to pee somewhere else, but he's kind of elderly, and it seemed kinder just to prevent him from peeing on plants I care about.  It's worked fairly well, though I can't understand at all why it's more satisfying, from his point of view, to pee on expensive plants instead of the mulch or the vinca and weeds that I have in an unobtrusive back corner of the yard.  He still tries to circumvent my blockade every once in a while, to get back to his most favorite place to whiz.