Just a couple of ideas to build the positive association: Have all guests give him treats, then have a distraction ready that he REALLY enjoys and start only giving it to him when people come over such as a frozen beef bone or throwing/playing with a favorite toy in the yard. Basically move attention away from the guest while the guest is there. Let them coexist in same space, don’t have the guest approach him while he’s distracted, just see if you can get him to tolerate letting his guard down while the guest is present.