Could be Australian Cattle Dog. Super, super durable, can do 10, 20, 30 miles a day no problem. Mid-sized dog. Easy-care coat, doesn't pickup much junk in their fur. Super smart, super protective. Some of them are the best dogs in the world, some can require extra attention.

Only drawbacks are that they can be too smart for their own good. You can't leave a dog like that alone in your house all day while you work, they will redecorate your house if bored. Some aren't crazy about people, other than their owners, some aren't crazy about other dogs at all.

Worth looking into for sure.