use a watermark and a digimark. delivering content in a non downloadable format or method will protect your content, but it will also cost you some members. i suppose it's worth testing to see if it's just a few members, in which case it may be worth doing.

btw, we have ex members return because they say they saved our videos and a few months after they cancel they see our watermark and that reminds them to rejoin. you might lose some of those rejoins without the watermark.