Just go to your profile page, scroll down to "Set My Account Inactive" and click. Should take 20-24 hours. You'll get an email when it goes inactive.
While inactive, you'll still be able to read messages and reports but nobody will be able to attack you. That's better than being locked out cause a lockout will stop you from logging in at all but won't stop you from being attacked.
TJ wrote:im quitting muel for a while, im really busy and theres not much to do yet. if you could lock my accounts for now, id appreciate it