Oh my goodness, I wish I lived near you! How tall is he? I know I'm really really biased, but methinks he looks quite sighthound-ish. Do you have a lot of Whippets in your area? He might even be Jack Russel/Whippie.

ETA: Wow, I'm on an editing roll today You mentioned he was quite thin. If he really is part Whippie (and I really do think he could be), he should be around that weight. Do you have a full body pic of him?