People in the past have tried to use "poor-man's copyright", which is
placing the composition in whichever format the original copy of the
composition is recorded or written, and having it mailed to themselves
with a time-stamp. The person can not open it unless it is needed for
proof in case they have to go to court at some point in time.

This "poor-man's copyright", (although the post office may time-stamp
the envelope) doesn't always work in court, which makes Sharyn's
advice necessary, if you are a songwriter who publicizes your work.

The guitar tab sites, bass, drums, etc. which publish copyrighted material have s "fair-use" argument. They post a message on each tab
indicating that they are "interpretations", and are for educational
purposes. There are sites that have tabs for instruments that aren't
even on the recording, and indicate that it is also for educational
purposes, yet the tabs they publish are usually the exact
compositions on the recording.
The major concern is actually preventing illegal downloading, and
figuring out a way to boost revenue on legal downloads, because the
legal downloads aren't turning out the profits they need. They will
probably turn their attention to those sites once they can boost
revenue on the downloads. For now, it isn't a major concern for the
record labels.