I LOVE a property with well maintained pet waste stations! The key is to have your porters/groundskeepers refill the bags every day because once they run out, their magic is lost on your residents
The place I currently live does a great job of being pet sensitive as well as curb appeal sensitive, and I've gotta say that their pet stations are a big part of this.
Also, Mark's right. Your folks need to be picking up after their pets. Their are city laws in most places about that regarding fines, etc. for violations. Check them out.
Though fines are a good deterrent, I found that positive reinforcement worked best when I was on site. I got my local PetSmart to donate toys, chew bones, etc. and then when I observed a resident being responsible, I would send them a thank you card for taking that extra step to make our community a much more beautiful place, and a toy/bone for their dog. That got HUGE responses! Even if you can't get the stuff donated, you can buy dog chews for pretty cheap in bulk.
Good luck!