Before you publish any song you'd better register it. In the Netherlands you can do this for free at the tax-office. They have a special section called "registration" . You hand them the music (paper, CD or whatever) and they register it for you. They will, for one, date-stamp the closed envelope containing your music you'll receive. Buma/Stemra can help you exploit your rights.

Any and all music you publish online can and will be copyed. If you don't want complete songs to be copyed, you can publish a short demo-version.