A useful gift is always appreciated by the dog owner and still gives you a wide range of items to choose from. The usefulness can be something the pet owner can benefit from or something the pet can utilize.
Natural organic treats or a pet fountain would be something a dog would like while a calendar or doggy coloring book is something the owner could enjoy. Matching or coordinated t-shirts are something both the dog and dog parent could enjoy!
The choices for useful dog owner gifts are unlimited so just do a little thinking and research and see what kind of useful (and maybe unusual?) item you can give as a gift.