T-dog was just a terribly written character, so it's good they just removed him, and Lorrie's death scene should have had more impact, but she was just so awful I just wanted them to get it over with.
T-dog's death was rubbish too - Carol had a gun, so why didn't he just smash the 2 zombies' faces in with it? Alternatively he could have just punched them both, or stabbed them in the eye with the gun barrel or just stuck his thumbs in their eyes. This is all ignoring his shoulder injury which didn't seem to bother him anyway as he was able to pin them to the wall with his arm which wouldn't have been possible with that shoulder muscle torn.
Also, why is it that Rick and Darryl carry knives, so they just stab zombies in the head/eye all the time, but T-dog didn't carry a knife? In a zombie apocalypse, surely you would carry a melee weapon with you at all times. They should have also had people doing patrols on the prison rooftops to check for breaches. Hell, they could have had other people sneaking into the prison and they wouldn't know it.
They also had the old, "silent zombies until spotted" thing where that herd made no noise until the gang looked at them. And there seemed to be loads of locked gates behind Rick, Glen and Darryl, surely they would just need to chain 1 in case they were overrun at the hole in the fence?