Any sort of legal verbage like that is “of tenuous value at best.” You don't have a piece of paper with an original signature on it, let alone a notary's seal. You don't even have solid proof of who the guy is — “he” could be a ’bot in Bulgaria, for all you or your computer knows.

So, all that you can realistically do is to program the site so that it presents reasonably-conspicuous notice of your terms-and-conditions. Do it in a way that reasonably avoids “plausible denial” and then hope for the best. Make sure that the entire manner in which your website presents and treats this information is supportive of your argument that “this is valuable property.” For instance, a valuable racehorse is locked in the barn at night and there are “no tresspassing” signs posted on the fence, at the very least. “Confidential” papers are stored in a locked filing cabinet, not a newspaper stand. (It will not matter if hackers “busted the lock” and got into the barn anyway. That's breaking and entering.)

So-called “exculpatory clauses” are no good at all if you committed a tort, or if a plaintff simply claims that you did. You can't excuse yourself from wrongdoing, or argue that “they ‘agreed’ that it was okay.” Won't fly.

Standing legal principles already exist to address some things, like defacement or denial-of-service or any other sort of intentional mischief, with-or-without verbage from you. In a sales or service transaction, a web-site is a whole lot like a vending machine. But if you are trying to protect a secret or an intellectual possession, get truly qualified advice. Hire an attorney who specializes in intellectual-property law. (Believe it or not, the fact that you spent money on an attorney, and followed his advice, is further evidence that what you're seeking to protect does, in fact, have material value.)