I am currently fostering a baby for a rescue. I can see why the rescues are picky. There is a reason that the dog is in need of rescueing. I have only had my foster baby for a little over a week, but I can tell you that I am glad that the rescue is very picky. They must get tons of applications, especially for yorkies. Not all applicants are like us and would love and take care of them as we do. Fences are important. That should be a major criteria, it would be terrible if the dog got out of their new home because the fence wasnt up to par. Not saying that everyone who owns dogs need a fence, but these babies are different, they have had a rough life and need that boundry. Most of the people that work with the rescue that go over the applications are volunteers. These people do not know you personally. I would say keep trying. Try calling them. I too have submitted applications with no responses. But I also understand that the people are volunteers and cant respond to everyone
good luck! Rescuing is wonderful.