Hello, I have the same problem. My dog's leg was almost impossible for him to walk on. He is better now but not the same. We couldn't figure out what was wrong, we took him to the vet and they said he was just getting old.
Months later my brother started working at a different animal hospital. He said that a common problem he was seeing in dogs in our area is a disease called anaplasma, that comes primarily from ticks. However we use tick medication, so we had ruled that out. Well, of course it can also be transmitted from nips by other dogs and dog poo, etc etc.., so he tested our dog using a test called Snap 4DX test, which tests for anaplasma and some other things.
Several months of antibacterial medication later our dog is better, but not the same. He had the disease for a while before being diagnosed and his leg is still kind of limpy.
If your vet hasn't done a snap 4dx test you should probably have it done. I see from your pics you live in a woodsy area like we do. Also once a day we give our dog two glucosamine w/msm pills from costco. The animal hospital where my brother works, the vets say that the Costco brand results in the most bio-available stuff in the dog, because it's not just about the mg of Glucosamine, but how much the dog actually absorbs.
On to my home improvement comments:
We have an elevated deck 7 feet off the ground. Our dog cannot make it up and down the stairs, either. The code here says that any ramps must conform to ADA requirements, which is insane for just a dog ramp; it means I have to have 90 feet of ramp (1:12). WTF nobody can do that unless you're rich and you have a contracting dream team or something.
Anyway I enjoyed this thread because I have searched a lot on google and I could never find anyone with a similar elevated deck type problem.
I am also planning to build a ramp, strictly for use by the dog. I am going to go 1:3 or less. Yes, you read that right, 1:3. We have a 1:3 ramp up to our couch and the dog loves it (he can't jump onto the couch anymore). The couch ramp has carpet for traction; obviously I'll need some serious traction for outdoors, that works when wet. I plan a 20' ramp.
I'd like to know how your deck came out. Some of the pictures you posted last year are no longer available via photobucket. That is a shame because I would really like to see what you had posted. Also do you have any pictures of the finished product?