The easy solution is for the link to lead to an interstitial that shows "do you want to view the content? It will be the only time you can do so.", and make the

The easy solution is for the link to lead to an interstitial that shows "do you want to view the content? It will be the only time you can do so.", and make the underlying HTTP resource unpredictable (e.g. different ID to the link) so that it cannot be directly addressed. It's a very common and easy to anticipate issue, I'm surprised that there are any one-time-link services left that suffer from it.