Copyright doesn't have to be registered to be legally binding here in Australia. Though you do need to be able to prove that you wrote it first. Years ago a professional muso here told me that he would mail himself a paper copy and a recorded copy of the song which he would then leave unopened in a filing cabinet so that the postmark could be used as dating evidence in any copyright claim. Joining APRA is a must if you have song performed in public so that you can get any mechanical royalties owed to you.

Personally I haven't written anything worth stealing.