You need to keep their little bottoms clean and free of any matting. Belive me I learned that the hard way.... its not pretty!
Every now and than one of mine will crowd around my feet and want to be near me at all times. That when I know there is a problem down below and time for a cleaning. They can get the poo bound up in the hair and cant go potty. ITs quit disgusting but can be prevented with normal grooming and trimming the butt hairs.