Big Paws Only Dog Forums

I have a 4 1/2yr old Rott he is about 104 pounds and in great shape.  He has had skin problems for the past couple years that has been making him itch constantly.  I have taken him to the Vet many times to address this problem.  I have givin him supplements like fish oils that came from a vet.  I have also changed his food and added missing link to his diet to see if it worked.  I am currently feeding him Eagle Pack Holistic Select Anchovy, Sardine & Salmon Meal Formula.  I add 2 scoops of Missing link and put a little water in plus a little wet food (he is a really picky eater).  I have been doing this for about 6 months and he goes in and out of itchy, dry, flaky skin.  Its really bad right now and I feel really bad for him.  Does anybody have any suggestions on what to do???