Well a better option would be encryption of UserID. as this will not only save addition of extra column in database but provide easy handling. Now the question is how will you do that.
Try this.. Make a simple encryption Logic (you can google this and just a few lines of code)
when creating that hyperlink, append that encrypted UserId . When user clicks , send that to server , decrypt and validate with the user id. this will help you to mange user on base of User Id which i hope is unique in you case.
Guid is just another option, why not using your UserID which is alreday unique :)