I'm surprised your trainer wants to lower the protein. With Rufus, he is completely nuts if he is on a low protein diet. We feed him raw meat and kibbles.
We feed him Burns which is an organic dog food. I noticed a big difference in everything when we switched to Burns. It is low on the additives the big pet food brands have (Hills, purina, Bakers, Iams, Eukanuba etc..) He just seemed healthier all the way around.
We also give him Prize choice frozen free flow meat (chicken beef or lamb) from Pets at Home. He gets fed twice a day.
There are those who swear by the BARF diet that is essentially an all raw diet that is mostly bones. The biggest selling point being a much calmer dog.
http://www.ukbarfclub.co.uk/about-barf-feeding/what-is-barf.php Rufus was fed on raw chicken carcusses at the shelter and did really well. It takes a lot of organisation to get it going but for those who feed their dogs BARF, they swear by it.