When Chalupa tries this again, instantly make him get off the bed (or sofa or lap or whatever.) Tell him 'off!' firmly, and point to the floor. It is important he makes the decision to get down himself, placing him on the floor is less effective. He is resource guarding, and the resource is you. Only allow him onto places of privilege (all furniture and your lap) at your invitation from now on. As soon as he so much as growls or wrinkles a lip at Gus, he has to go down. He will soon learn that this behaviour loses him what he wants most, which is to be next to you.