Strange odor?

Nanook my 13 year old mix (Shep. & we think possibly husky/samoyed &/or wolf) has been getting a strange odor to him the past few months. We have visited our vet many times (& I was a vet tech for years) & are begining to run out of possibilities.
It is kind of a weird smell, it does NOT smell like hot spots, anal glands, rotting, bad breath or wet dog. Just a bad odor. The odor is not comming from a paticular spot just his whole body smells. It keeps getting worse. There are NO skin irritations of any kind at all (no redness, flakes, sores, lumps or bumps, etc..).
We have tried a couple different prescription shampoos & topical sprays. We dry him very well after a bath & he is always well groomed. At first after a bath he would smell good for a few days now he smells bad about 5 hours after the bath. We have tried to wait longer in between baths, even though I dry him very well we thought maybe too many baths would make it worse, even though that is what is reccomended by the vet & shampoo. Before this he would only get a bath about 2 times a year, only when needed. He is not allowed to swim in lakes or streams until we get this figured out so I know it is not commming from bad water. We also tried him on antibiotics.
He has been on the same food for the past 3-4 years, nutro natrual choice senior.
He is going to get a full panel cbc blood work done in a couple weeks (although he just had one in late April & everything was PERFECT then). But just to double check it.
If anyone has any ideas or had something simmilar happen please let me know.

I guess it is almost like a combination of all the smells I listed (wet dog, hot spots, rotten) but not really more like one or the other.
I have smelled it before on other older dogs when I worked at the vets office & most were cured by shampoos & antibiotics, some passed before we could figure it out & unfortanatly some owners did not want to try to treat the smell.
At first I just thought "oh well an old dog smell" but this is getting bad.

I have no idea who could be causing this, but if you are
going to take him in for further blood work, I think that's a
good start to finding a cause or cure. Is your dog an inside
dog? I mean do you know exactly what he eats or doesn't eat?
A food allergy,internal infection or bad teeth/gums could be some
causes. Good luck with this problem.

I know people develop a bad odor when they have kidney or liver problems. Possibility??

Well his bloodwork was done this am & it is PERFECT. the vet & I could not believe it for such an oler large dog.
We are switching him to different food & see if that helps. The odor is not quite as bad but it still there & easily smelled. He is an inside dog unless to potty, he is w/ me almost 24/7... he even goes to work w/ me. I know everything he gets into & that is nothing.
He does have a fatty tumor (that was removed a couple times & keeps groing back eventually) & another tumor that we are unsure of so that was biopsied today too. We should have the results in a week or so. But the vet really really doubts that that would cause an odor at all.
I guess if the food does not change his odor than it is just a really bad old dog smell.

Good luck on the results of the tests on the tumor. The idea
of changing foods is a very good one. If his blood work is good
and checks out o k at the vets health wise, then maybe this will
help. You might try sprinkling some baking soda on his coat &
brushing it through the hair. It might cut down on some odors.
Let us know how things go & best of luck with this.:)