I have modelled the dog and I have found some noises that would go with the dog. There will be fly noises its going to be like Charlie Brown were he always has a horrible comfort blanket that you can sense it smells so i've found some fly noises aswell to give the effect.

Website:-
www.sounddogs.com
animal,dogs,one running about and barking.
flies (first one in the list) the noises are realistic which work to effect.
Because the other character dont talk theres going to be just mumble noises. Keeping him the grumpy teenager and that they dont speak alot. But he might speak a little to the dog. Because the dog brings out his personality that most of the time is hidding behind a shield. But in his own way.