What dog only needs about a half hour to an hour walk a day?

[Louccby]

The dog would be left on its own for about 6 to 7 hours for 2 days a week and usually about an hour or more every other day in a medium sized backyard in suburbia. Our backyard in enclosed by a fence and surrounded on all three sides with other houses. I'm planning on getting an 18 month to 2 year old dog from an animal shelter. I'd like a medium sized dog with a coat that would only require grooming about once a week. The dog won't be allowed inside the house unless there's a storm or fireworks. I will walk the dog for about a half hour to an hour once a day. No elderly people stay with us and only visit on christmas and birthdays and stuff. The dog will be a family pet but the age of the main owner is 15 and the youngest child in the house is 10. The owner is not very active but would like a slightly more active dog so that they can get more exercise. I don't want a guard dog but a dog that would bark to warn people away would be nice. I have never owned a dog before so wanted to know what dog would fit in best with our family's lifestyle.