We discovered when Spock was a young puppy that he was too short to reach the hole, then too big to fit through it (thank goodness). Miss Bones may be a tiny girl, but she hasn't figured out a way to outsmart the hole yet.
They've torn down wire mesh covering the hole several times, so this spring, my boyfriend is going to build a wooden cage over the meter and the hole in hopes of Bones being less agitated.