"Basic" encryption is simple enough but DVD videos are not so easy owing to DVD being a known spec and the spec not affording such measures (to my knowledge). Making it as good as normal is quite hard but making you can however do fun things to make the DVD all but unwatchable. Any protections are a) designed to prevent copying not watching and b) useless as you well know)
A PC player (or something like xbmc capable of ignoring the spec as you tell it to is an advantage here).
I also recall the DVD quiz videos "popular" about a year ago were slightly different but I know of nothing to do anything with/about them.
First things first sound:
find a sound you can not take and add it to the audio track (good chance it will be high pitched too). Wipe it out with the equaliser. It will probably sound a bit odd though if you wipe out the high range and I am fairly sure it is not a good idea to play extended high sounds on average speakers).
Sound 2: DVDs have the option for several audio tracks: split it up.
Subtitles: DVD subs are actually pictures and they have a "forced" mode (usually used for one or two lines of audio in another language). Need I continue?
Picture: most players have a decent zoom function. Border your input video (if especially flash you can change the borders as the film goes on) and use it.
I would say look into multiple angles in a manner like the multiple audio tracks above but not much in the freeware world exists for it. If you do go multiple angles you could get a crude steganography thing going on.
Picture 2: colour. TVs have decent colour changing ability, use it (drop brightness etc and fix with TV, I recall you mentioning a more modern TV is what you were planning to get and chances are it has a custom profile ability).
Video: One of the more recent copy protection methods is to add junk to the video and while a freeware version of such a thing exists (doom9 forums about 2 years ago now, I recall a phrase along the lines of I hope my boss does not see this from mug_funky being used in it for the curious) it will serve no purpose here (see a) and b) above), a single sided single layer DVD is capable of about 2 hours video (3 would be pushing it) but a simple black frame takes very little space to encode.
Add a list of good chapters at key points and bury such a list somewhere deep/hidden in the menu.
Speaking of menus: extras/easter eggs are a good way of hiding stuff.
All in all you can make a really horrendous to watch video which would not stop a determined person but someone without some technical skill would have their work cut out. Completely useless for commercial stuff mind you.
There are probably several more but my sleep deprived brain is not working so good right now.
Tools (which I am fairly sure I have linked you in the past), my usual DVD kit of avisynth+DGmpegdec, PCGedit, vobedit, ifoedit and whatever sub app freecodecs has that you like (look back through my DVD related posts for more). None are especially easy/nice to use compared to other editing tools (damn powerful mind you) but I imagine you did not expect it to be when you asked the question.
