All of my domains are locked. |rasta| On my registrant they have an option to "lock" and they aren't expensive.
The lock unlock option reads: Locking a domain adds an additional step of security if you wish to make any changes to your domain. It prevents you from accidentally changing records, such as nameservers and contact information, without first unlocking the domain. It also automatically rejects requests to transfer the domain away from our registrar at the registry level.
Locking a domain does not prevent someone from unlocking the domain and making changes from within the control panel. Your most important security measure should always be to not share your password with anyone and to change it periodically.