*side note to answer a question*
Yes, Rusty has been neutered, but it wasn't until he was several years old and had been used for breeding. I also have a breeding female in the house so I'm sure that has a lot to do with it.
He is kennel trained and goes in the kennel at night. I can't leave him in a kennel all day and the second he is loose in the house he makes his rounds to mark. You cannot take your eyes off him for a second which is what happened yesterday when I had a child in charge of watching him. Bad idea.
I really think the play pen would work nicely. I have plenty of room and it would put him out with the family in a comfy bed. Not really any different than lounging on the couch except I don't have to keep an eye on him. I believe Rusty is 6 (I need to look that up) so he mostly sleeps all the time anyhow.