As Carol said, put everything in writing! I co-own Dexter with his breeder--that was her condition for full registration so I could show him. Apart from a formal contract, we had an exchange of emails laying out what our understandings and expectations were. Sometimes hard feelings arise out of co-ownerships. I would say that ownership arrangements should reflect a relationship of mutual trust and understanding, not substitute for it! And I found it really helpful to have an informal conversation exploring as many possibilities as we could think of, e.g., I wanted to be able to bail on the show thing at any time and neuter him.