For cat poop, we got one of these dog playpen enclosures: Amazon Basics - Octagonal Foldable Metal Exercise Pet Play Pen for Dogs, Fence Pen, Single Door, Small, 60 x 60 x 30 Inches, Black a.co/d/6Nz4VuU
It is set so that the cats can get through a gap easily, but Henry can’t get his head through without causing a huge racket.