I have a CHI and she does the same thing. But since I go to school, I leave her in her kennel, and usually when I get home her pad is all messed up and sometimes shredded. But when she is running around the house it does not get shredded (we have a pad in the living room), so maybe your puppies get lonley or bord. Do they do this when you are next to them? Maybe you should give them something that will occupy them, like a rawhide or a greenie. It might work.
