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Small dogs can be great, easier to handle, takes up less room in a tent, lots of energy.
The border terrier is probably awesome, but 15 lbs is really really small. That's toy breed territory.
Honestly just get a medium sized mutt. Get something athletic, and train him well. Find an animal shelter or rescue. I've always said an adopted dog seems to bond closer to its owner after being recued, they just have this way when they've been rescued, it's awesome.
Get a young dog, or even a puppy (be advised a puppy is so so so much work for the first year, it kinda sucks) train him, and he'll be great.
