Personally, I've yet to see a scenario that grass within "city limits" works. However, if one could do a script to make Pokemon appear in urban areas, such as in alleys, it would be interesting. FR/LG has "urban" Pokemon in the pokedex, such as Meowth, which coincides with alleys and such (you'd see cats, mice, and the occasional bird or dog in alleyways of almost any major city in real life). tall grass just doesn't fit in towns, but that doesn't mean there can't be alternative methods to wild Pokemon in such areas.