Well, making a mobile defender type is good, but thats something 4e got the rough idea of at least. If you have a defender, theres really nothing keeping more mobile higher level foes from just going around him and to the squishies, while tanking, like healing, is just buying time as opposed to ending threats.
A shield fighter needs some credible offense in addition to a better defense than most, as well as some means of forcing opponents to remain engaged with him might help, whether by keeping up with the opponent, locking him down, or by intercepting attacks effectively(perhaps while hes in reach of the opponent, he can disrupt the attack, whether by providing cover or breaking line of effect, or by laying down stuns, trips and dazes).