Collecting a response without requiring log in - one time URL? Issues with false positives

Background and Problem

I have a system that has core users augmented by some minor contributors who only need to be able to provide approvals for certain things. To support this, the system reacts to database changes and emails those approvers with a single button in the body of the email. This button is just a link to a unique url - something like https://myapp/response/12345-abcdefg-6789.

That "response" page is listed in the web config as not requiring a log in. Thus, the approver should only have to click on the link in the email, and the system should detect that and mark their response.

In all of our testing, this works great. All we're doing is marking the response via the page's code behind, and then displaying a message on the page that the response was received. On the surface, this seems like about as easy of a task as you can dream up.

However, we're getting false positives in production. The approvers are telling us that things are being marked as approved when they never clicked the link. I assume this has something to do with their browsers checking the links for safety or something - and by performing that safety check, it's triggering the system to record the response. Unfortunately, i haven't been able to reproduce this - even when we have some of the approvers on the phone while we try it.

The question is - what is the best strategy to avoid a false positive with buttons in an email?

Lots of companies do this kind of thing - i'm looking right now at an invitation from a friend via evite. It has Yes, Maybe, and No which appear to have the same kind of setup i described above.

Is there something i should be doing with redirects after x seconds? Is there some other javascript i should be deploying on the page? Is there some other potential cause for this? The IIS logs seem to indicate that the "fake clicks" are coming from the target users computers. Which is a bit of a relief, since it's hard to imagine how some other external machine could end up at a GUID based url that is not represented by a physical file that could be crawled over in some way.

I would like to avoid having another button for the user to click, where they would click "Approve" in the email, and then when they get to the page they have click the same thing again.

Thanks!