This is from ESPN Rumors http://insider.espn.go.com/nfl/features/rumors
Al Harris cleared waivers Tuesday afternoon, and was free to sign with any NFL team. By Wednesday morning, Aaron Wilson of National Football Post had reported that Harris has signed with the Miami Dolphins, per agent Jack Bechta.
Harris did a number on his left leg on Nov. 22, 2009. On that day, he tore the anterior cruciate ligament, the lateral collateral ligament, the IT band, the fibular collateral ligament and the lateral hamstring. If you're considering a hunt for any other players that have suffered the same battery of injuries at once, good luck.
As such, it's hard to say whether he's fully back to form. In order to sign, he needed to pass a physical, but that doesn't guarantee that he can perform at a high level. Even so, Harris does provide some veteran depth for a young corps of CBs.