Yeah, problem with this, there's a lot of ways to get stolen.
The old "don't frame us" trick, in JS:
<SCRIPT LANGUAGE="JAVASCRIPT" TYPE="TEXT/JAVASCRIPT">
<!---
//we don't wish to be framed!!
if (top.location != self.location) {
top.location.replace(self.location)
}
-->
</script>
Dunno if we still need worry about that one or not...
I sometimes do a check of $SERVER['SCRIPT_FILENAME'] as well, but that's just basically to insure that no one grabs an include file as a seperate page ... doesn't help much on folks who steal HTML...