Gas, Bloating Mystery, please Help

[crosbydog]

My dog Crosby is a 4-5 year old Lab mix. he was a rescue dog. He has some chow in him (spots on his tounge) maybe some shepherd., he is small for a lab only 48 pounds- he is lightly built but very athletic.
Ever since he has been about 1 year old we have had an increasing problem with gas, I have switched vets and asked them repeatedly for help, I have worked with a holistic dog nutritionist but no one has been able to solve the problem or really take me seriously. Please help me. I am beginning to get very worried.
Here are all of the details:

Primary gas time: after his second daily meal- from 7:30 pm to 10:30 pm
but it can be bad any time, usually never before noon though.

Symptoms: flatulance consistantly every 4-5 seconds sustained for 1 to three hours, 75% of flatulance does not smell at all, 25% smells horrible, occasional loud belching, very loud stomach sounds, can be heard within a three foot radius, very bloated stomach, (normally, crosby looks like he is on the thin side of healthy, with a marked indentation where his stomach is, when he is bloated his stomach bulges 3'' past his ribs),

Normal Routine: he eats 3 cups of food total daily, split between two meals, Lassie brand natural food we switch between chicken and oatmeal and lamb and rice, he has a special food bowl that has molded raised areas in it so he has to slow down eating, he gets 1 table spoon of stoneybrook orgainic plain low fat yougert with each meal and a cap full of olive oil with each meal, he drinks water from the toilet when he pleases during the day, he runs or swims playing fetch for 15-30 minutes twice daily, once after breakfast and once after dinner, during which he has a bowel movement- always normal.

Remedies that have been tried but found unsuccessful either made no difference or made the problem worse:
Foods- started with purina one lamb and rice, then wellness complete health whitefish and sweet potato, then wellness core whitefish the wellness products were fine, but kind of made his gas smelly and his breath smelly, so I found the lassie at the supermarket- no corn, no wheat and it is CHEAP (although I add olive oil to supplement)!
I have tried using dynovite as a food suppliment- went through one of the big tubs of it with no difference.
I tried fresh garlic cloves- no difference.
I don't know if the molded food bowl works, but I have continued to use it.
He dosen't get scraps
He dosen't get raw hyde
I went to the vet again today and he suggested adding pumpkin.

Please, if you have any ideas, advice, suggestions or suggested diagnosis for what is going on with him please respond, this poor dog looks miserable for hours every night when he is inflated.