The enclosure is a little small for bushes, as I need to be able to mow and get the snowthrower in there. I did just plant some Valerian in a corner, so we'll see how that goes.
Maybe you can plant some bushes in the enclosure ? My Willi and Morris loved to sleep under the Japanese Maples, they look nice, red or green leaves, grow like an umbrella and are very frost resistant. Or lilac ? Very frost resistant, too. And then maybe plant 3 of each in a group ? Will look great and there will be more shadow for the boys.