Yea - this is great news. Okay now on to the mulch. Do you know what kind of mulch you have down? I hope it is not cocoa beans as this is especially toxic to a dog.
http://www.aspca.org/site/PageServer...licationscocoa
You might try spraying bitter apple (petsmart has it) if he always goes to certain spots but what I would do is get him other outside toys so he is not even interested in the mulch. I would also have him on a leash and work with him on not going to that area. Yorkies love soccer balls and maybe you can play with one outside. Take his focus away from the mulch.