The dog is a pet in Harvest Moon: Save the Homeland.
Unlike most Harvest Moon games, you don't automatically own a dog. You have to befriend a dog in the village by leaving food in the dog food dish in your front yard. There are two different types of dogs to try and befriend. Once you have befriended the dog, you can pick it up and it will give you the option to keep it and if you pick yes, you will be able to name it, and if you pick no, you will just put it down.
The dog has little use at first. The player can only feed it and pick him up to show to villagers. To keep the dog from getting sick, you have to carry it inside your house when it is expected to rain the next day, however you will not need to do this once you pay Woody to build you a dog house.
The dog is very useful once its affection is high enough as it can be trained with the flute. A trained dog can follow you around, jump over fences, or even herd cows in and out of the barn. A friendly dog responds more often to flute commands and runs faster, and will be able to keep up with you as you run (with the exception of you riding your horse around town.)
There are no festivals that require your dog, nor is your dog useful to scare wild animals from your farm at night.