Best way to fix the OT issue is the draft. Problem is you cant guarantee the prospect will work out, you cant be sure there will even be one to choose worth the pick, and you cant even be sure if they will be able to start immediately if you grab a guy who can play. That brings in the stop gap veteran, the guy you can hopefully trust for minimum one year without breaking the bank, but who could surprise you. Oher is a perfect example of that guy. He actually has more than one year experience playing LT, and has shown at one point he could play it at a decently high level. But at the same time if a rookie comes in and out plays him and ends up starting you still have decent depth.
The key is the dollar amount Oher is looking for...