Got your back achievement
I struggled with this achievement because one way or another Shadow would die (stupid dog kept running into the line of fire), but got this achievement today.
I played the last level on cadet ( was only playing for the badges) and it popped up at the end of the level. Im surprised because the bit where your sniping about half way through the level I saw Shadow die but it didnt go against me. After that just keep him alive and do the last fight and it should pop up on the score page. It was the best level for me because you get Shadow back near the end. Loved the dog but sometimes he was just annoying.
Hope this help for anyone else who is struggling getting this achievement.
Now I need the 'Finish him shadow' achievement, which I dont know how to do. Any help?