Little do they know, tunnels are much more effective when they are a) underground and b) not transparent. Good first attempt, kitties, but better luck next time.
From the submitter:
Building up a gate to keep our dogs in the yard. Yes, those are shipping pallets on top of the gate, and yes that is yellow electrical tape holding the pallets together. The green parts are several dog poo disposal bags tied together then used to lash the pallets down when we ran out of yellow electrical tape.