There are helpful tools to keep a sub humble.
Simple CBT. Just pull harder to correct the sub.
Looks like CBT time. Where to start?
Instructing the sub on how to greet the Dom is a good way to keep it humble with only a little bit of humiliation. Of course, a pants hanger used as a humbler can do that as well.
It's already locked. But adding a humbler behind its legs is definitely an attention getter when its balls start getting stretched.