If you go back to Knuckle Kids original post, you will see that he is referring to hiring a PSE and executing releases, etcetera. I would agree that those formalities might not be necessary as long as "home movies" remain strictly in ones hands and are never distributed. Query, though, whether dispensing with formalities such as commercial releases might not create criminal liabilities under anti-prostitution statutes?
If you take someones picture naked/having sex, you will need copies of ID and certain information about them based on Federal Law. You may not need them to allow you to release it commercially, but if you have it in your possession, you can be required to show they are of legal age. You must be able to prove you don't have child porn.
How long time and how many positions does that fee cover? If this is the rate for shooting porn I will immediately start searching for some investors :-)
Solution: Having the client sign a contract stating that publishing the movie is a big no-no. But if the price is right I also belive in honest handshakes :-)
The short answer is there's nothing you can do to prevent them from releasing the video. It may not be legal, but most of the tube sites are illegal and they still operate. They would have a more difficult time getting paid for the video, but they could easily release it on the internet. If you don't want it released, don't make the video.
The best answer you're going to get here is this. If it's that big of a deal, just don't do it. Contract or no contract, if they get a wild hair up their ass at some point in the future, they're going to do what they're going to do and you might not even find out about it until years later. If you make pictures, videos, anything that is recognizably you it might end up online. People are simply not to be trusted. I made a sex video with someone I was dating once (This person was very reluctant to do it out of fear it would somehow get out) and never put it online (and never would) but that's because I'm an honest person. That person is just plain lucky. They trusted me but they didn't have any way of knowing if I was really as honest as I said I was. Even if you can make a legally agreement with someone, if they end up putting it online, nothing you can do after that is going to undo it.