I finally got around to Zeppe proofing the shed. Basically, I don't want him to go behind it or under it when I let him roam. Thankfully, there were some cinder blocks and pavers in the shed. One cinder block with a paver on top is blocking off him crawling behind it. The other side of the shed that faces a fence has a bunch of old timbers back there. I took out one of the timbers and used it to block off the underside of the shed facing the birdbath garden. The yard slopes, so there's a gap there. Two more pavers got propped against the ends of the timbers. I hope that's enough.
And on the plus side, my rhodadendrons are finally starting to bloom. :)
I had to hang outside the front window to get these.