Copyright fights, as with most conflicts in the mainstream music industry, are almost universally won by the party with the deeper pockets.
That said, there are things anybody can and probably should do to protect rights in one's own music no matter who you are.
Rich Stim, guitarist of MX-80 and California attorney wrote a book for Nolo Press a few years ago called
Music Law. I highly reccomend it.
It explains the various rights that are protected and how copyright law works. There are several surprising parts in it. For example, copyright protection under the law doesn't begin with the filling out of a paper form or other bureacratic instrument; the law says it exists the moment a completed work is put into a fixed form. From that very second.
Its an interesting story how you get from that legal reality to Jon Fogerty being sued for stealing riffs from...John Fogerty.
Stim's style is great, and is clearly written from the persepctive of an original band musician.
-r