how old is he?, if he is under 6 months then you would expect this behaviour as its all part of growing up, if he is an adult then he was probably never taught not to in his previous home. there have been some excellent answers to this problem on this site before and I'm sure someone will be along soon with links to these, or you could try "puppy biting" in the search facility. Im intrigued to knoww hat a GSD corgi cross looks like