The requirements of said garden (surviving pollution, foot traffic, and worst of all, dog pee) make this a nearly impossible situation for a perennial garden. But there are some toughies I have seen in urban plantings like the one you described, so here goes...
Dog pee is the biggest enemy here in my mind, so acid lovers are a must. Heuchera 'Montrose Ruby' would give you a nearly evergreen (maroon, actually) foliage. Dicentra 'King of Hearts' blooms the whole season longwith a soft blue foliage that would contrast nicely with the maroon. Woodland phlox (P. divaricata) would even lend a touch of fragrance (you pick the flower color of your choice, as long as it's red, pink, white or blue), same for primrose (Primula spp.), for a great spring color shot, and Hosta 'Alan P. Mconnell' is a great dwarf hosta (green with a white edge) you could scatter around the rest (you could use H. 'Gingko Craig' for the same color or H. 'Kabitan' for a yellow and green leaf).
Howzdat? All of the above take shade, although I'm not sure on pollution tolerance for all these plants. Let me know how it turns out (pictures would be nice...)