Have to resort to watermarks

I have a YouTube account with several 30 minute videos that a Hulu-type (though it's not Hulu) keep stealing. So I'm going to have to resort to putting watermarks on my videos, but I don't know what I should put. It needs to be something that will scare these guys away, or at least make the video unsuitable for them to play it back on their site.

I know I can probably use my name in one of the bottom corners, but I'm also wondering if I should try to use a little trickery to scare them and put something like "Property of Defense Department or something like that. Of course I'm just using that as an example, Any recommendations?