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Yero, There is no sure way to stop copying. There are various encryption scripts and cheap ways as alreday stated above, but if someone really wants the material, they will get it very easily.
Best advice I know is to
1- Display a copyright notice, in words, in full on each page.
2- Allow visitors to reproduce your work but say they MUST include your credits and a link back.
Many sites do this as a compromise and also to help link popularity.
One other trick is to display material in PDF. Of course it can be copied, but not so easily if you disable the edit function. It may just be enough to disuade unscrupulous visitors.