Renteria has had such a strangely unpredictable career, I don't think he's a guarantee for anything. He started out his career nicely as a young guy, improving in his early 20's until he had a major setback season at age 25. Consecutive career years during the normal peak period, 26/27, were followed by 2 more down years, and now he's putting up back to back very good seasons. As an aging middle infielder, I'm not sure how much time he's got left where he'll be effective there, and if he ever has to move, his value will plummet. The closest thing he can guarantee, though, is not being a black hole. His worst year is no better than what the Cubs are getting now, but his other off years would at least be middle of the pack for SS productivity.