Cats, cats, cats galore... what to do about it?

[Andrew S.]

The neighbor of one of my rental properties has about a dozen cats.  Evidently, with that many cats, litter boxes are not practical, so unfortunately, these cats get kicked outside to their "business".  As it turns out, they seem to have decided that the front yard of my rental property is the proper place to take care of this and while the yard is big enough to accommodate the occasional "transgression", 12 cats generate a huge amount of waste - to the point where there is a permanent stench at my front door.  The neighbor on the other side of my property has told me that the folks with the cats are very defensive when approached about any problems related to their felines, so I have not yet approached them directly.  Before I do, I wonder if anyone here knows of any ways to "discourage" the cats from using my front yard as a bathroom.  I suppose I could run a fence between the properties but cats can be very stubborn and they will, of course, find a way to get around it.  I also could call the animal control people (I believe it's actually against code to let cats roam in the city - though nobody tends to enforce it), but that probably won't endear me to my neighbors much.... 

Don't get me wrong, I love cats, but this is out of control....  Any thoughts?  @Brandon Turner ?