While we all wait with bated breath to see what avatar sidders will choose, I thought a few suggestions might come in handy to help the old boy out. Here's mine.
My bet is no avatar at all, old age and technology don't mix.
Lots of dogs in avatars on this board.
Hard to tell with a small photo and nothing to scale against but that looks to me very much like a sable & white Smooth Collie (short-coated version of the Rough Collie, of which the best known example was Lassie). Am I close?