I have my 2 yorkies and a 14 yr old cocker spaniel mix. I have never had any problem with any of them messing with the tree and/or ornaments. In fact, laying under the tree used to be a favorite spot for my older dog. If you're concerned, I'd just keep an eye on them and the decor while you're home and when you're away, I think the x-pen around the tree sounds like a great idea. Here's a few festive Christmas pics to get you guys in the mood....