http://www.marapets.com/petexchange.php?do=doaccept&id={petid}

You need to tailor it for each pet. Replace the {petid} at the end of the link with the specific pet's id.

You find the pets id by clicking on the pet to view it's profile and looking at the address in your bar and taking the number that appears at the end.

For example take my Chibs MIshia. The link to her profile is http://www.marapets.com/pets.php?id=646472 so therefore her pet id is 646472.