Would suggest using a diff tool to do this.
However, if you were willing to put the coding in, you could add their Expiration Date and then have the page display nothing if their expiration date is before the current date. Suspect that could be hacked easily though.
I have also found that PayPal isn't the best at redirecting back to the correct page.
Marketo isn't capable of expiring links.
Thanks, Josh! Are you aware of different tools that you can recommend?