peeing on my dad...

Jaxon is completely housebroken and has been for the past 4-5 months.  Over the holidays he did have several accidents only when my house was full with company.  We thought this may have been because his "signals" to go out are very minimal (he usually sits in the kitchen doorway and stares at one of us).  Because we had so much company, it was hard for him to give any known signals and most of the visitors either didn't pay attention to him or mistaked sitting or laying near the door as his signal to go out.  Going out some should have helped but for whatever reason, Jaxon seems not to empty his bladder every time.  Anyhow, now that the holidays are over and life is back to normal, Jaxon is back to being completely housebroken.  The exception to this is when my dad comes.  My dad is a boisterous person who instantly makes a fuss over my boys and my dogs when he walks in the door.  I would agree that if Jaxon peed on him when he first came it was due to excitement, but this isn't normally when he pees on him!  He waits until he's been at our house for a while (and my dad and the boys have calmed down), then he goes over like he wants attention and when my dad starts petting him, he pees.  He's not lifting his leg.  Also...Jaxon occasionally peeks his privates out when my dad comes or when he pets him.  I don't have a clue what to think!