A couple people (including myself) suggested you have him genetically tested. I just thought I would add that many articles are written on this subject and it's not a perfect science. They say to pick a place that compares your dogs DNA to the most dog breeds.
I read an article the other day about a woman who basically got three different portraits of her dog genetically. She called the practice a scam.
Even Universities can get it wrong if they do not have the proper bank to compare with. http://www.thetelegram.com/News/Loca...Newfoundland/1
You could ask the company what kind of bank it has, how many breeds it will test for.
Although some people claim they can rule out the possibility of certain genes being in your dog with one look, this too is a sham. We can just give an educated guess about what dog contributed to the phenotype.