Lockdown doesn't require password unless your device settings require password -- it normally just kicks it back to requiring pin. Which is still quite secure. I don't know what you mean saying it is disabled by default -- it is available by default if you long press the power button and click Lockdown.
Even better is to reboot the device. Then it will be in lockdown mode -- pin required -- and also encrypted awaiting the pin. A modern device fresh from a restart should be quite hard indeed to crack without some alternate access to the person's Google account.