Well, a very high quality (in terms of ingredients) food that is aimed at allergic dogs would be a good idea. But you'd need to make sure that he didn't get hold of anything else - most especially things with wheat in them (eg. bread or pizza) for it to be truely effective.
As a general rule, the point of allergy foods is that they're simple. They don't include any of the cheap and nasty grains that commonly cause allergy problems, and the meat protein source is usually an "exotic" one. Exotic simply because it needs to be something that the dog has not eaten before, and therefore won't have pre-exiting anitbodies against (allergies being an abnormal immune system response).
So. What meat protein sources has he eaten before? Chicken and lamb,, presumably, and duck briefly. Anything else? Because they should be avoided... How about fish? Has he had a fish-based food? Or venison?
A good food to try him on would be something like Wellness' Simple solutions range (comes in either venison/rice or duck/rice formulas), Solid Gold's Holistique Blendz (fish/potato), or Natural Balance (duck/potato, fish/sweet potato, venison/rice formulas).
All of those foods are suitable for a dog with severe allergies. Their websites, each with store locators are posted below:
http://www.oldmotherhubbard.com/dogs/simple_food_overview.html
http://www.solidgoldhealth.com/products/showproduct.php?id=6&code=160
http://www.naturalbalanceinc.com/dogformulas/PandD.html
If he's OK with those foods (and it will probably take a couple of months or more to know for sure), then a better long-term bet might be one of Fromms Four Star range - which is a better food, but also contains a greater variety of grains, which isn't ideal when you're trying to establish cause and get his skin sorted out.
If those foods don't work though, would you consider trying a natural raw diet? That is one pretty sure way of narrowing down precisely what the dog can and can't eat. It's usually also a lot less problematic in respect of digestion and skin issues that are often the result of plant proteins - which is pretty hard to avoid in a kibble.