Comment 2 for bug 1563611

This will be partially addressed by https://github.com/juju/juju/pull/5048. When you have a non-empty hosted model, you'll get:

"""
juju destroy-controller ctrl
WARNING! This command will destroy the "local.ctrl" controller.
This includes all machines, services, data and other resources.

Continue [y/N]? y
ERROR cannot destroy controller "local.ctrl"

The controller has live hosted models. If you want
to destroy all hosted models in the controller,
run this command again with the --destroy-all-models
flag.

Models:
        admin@local/default (alive), 1 machine
"""