[Breeds] Any breed suggestions?

Coop the FluffWe adopted our pup Cooper about 4 months ago from a local animal shelter. He was entered as a stray because the guy who dropped him off didn't want to pay the surrendering fee, so we know very little about him. They said he was about a year and a half old and was a dachshund mix.Since taking him to the vet and showing pictures to family members with breeding experience, we have been told he is probably younger (closer to 8-12 months) and more Jack Russell than Dachshund. We have also gotten Basenji. His proportions are a little wonky (shorter legs, longer body) but he totally acts like a JRT. Very smart, easily learns tricks but incredibly stubborn (won't do anything unless he knows he's getting something in return), and incredibly territorial with us - anyone or thing that comes near us sends him into a total barking meltdown, though we are working on training him out of this.Some additional info: Weight: 18 pounds Activity: Incredibly energetic, can run for miles without stopping (literally) Height: 10" or so to shoulderIf videos of him moving/interacting would be helpful, I have plenty of those, too!TIA!(edits for clarification) via /r/dogs http://ift.tt/2rXK1sE