The answer depends on the pet’s age, temperament, and activity level. A laid-back Lab, especially one with a few years under his belt, might relax on the sofa all day, then greet his owner at the door, tail wagging. A more energetic canine — say, a young terrier — may quickly grow bored and find mischievous ways to entertain himself, like chewing shoes or treating neighbors to a bark-a-thon. Every dog handles solo time differently. Having said this, most dog experts recommend three hours for a puppy and six hours for an adult. When you know you’ll be away longer, investigate doggie day-care options or ask a friend to come by and take your pet for a walk. And anytime you leave you pooch alone for a few hours, provide a fun distraction: Food-dispensing toys and Nylabones will keep him engaged — and busy paws are happy paws. Also, think about how often your pet needs to relieve himself. It’s not fair to expect him to “hold it” for hours on end; the more frequently a dog is forced to, the more prone he’ll be to urinary tract infections. And in case you’re thinking, I’ll just put the pooch out back, let me say this: Leaving a canine outside is never the answer. Even a good fence won’t protect him from dangers like severe weather, heatstroke, and predators. Too much can go wrong when your pal is left outdoors unattended.