You'll probably get all sorts of answers to this, but the only copy protection I'm familiar with is provided by Adobe Encore. However, they say it only works if you farm out the duplication to a production house.
In actuality, the macrovision, or whatever it is that prevents analog copying (VCR tape) works a bit. It makes the picture go light and dark if it detects a VCR in record mode, in the loop.
To prevent disc duplication by programs like Nero, there is a home-made process you can do. I've done it and it really works. Of course, people who know what to do can still grab the vobs. The process is detailed on a British site. I forget the url though (sorry) and there's some work to do in your production, but the short of it is you create a separate mp2 file of a particular length (I think it was ten minutes) and make it be the final file. Then you scratch two arcs on the last 1mm of the recorded part of the disk, using a jewelers screwdriver. I had it down to where I could scratch about a five a minute.
Even then, I never sold extra copies of wedding videos, so I finally gave up and started giving them a bunch to start with and I don't mess with copy protection on those any more.