If you've heard it before, it's worth repeating. If you've never heard it, take note: A tired dog is a happy dog. Not enough exercise--either mental or physical--is at the root of most behavioral (and many health) problems.

Mental stimulation

Mental stimulation is important to the development and happiness of any pup, but it's absolutely essential for dogs who are left alone for long stretches (such as when you're at work). Suggestions to keep her on her mental toes:

• Kongs. There are many interactive toys on the market, but Kongs are one of the classics. A beehive-shaped piece of rubber with holes at either end, its sole purpose is to keep your dog busy. Fill the Kong with cheese, baby food, milk bones, or any combination of dog-safe treats, and she'll smell the food inside and use her mouth, tongue, and paws to work it out.

  Start with treats that fall out fairly easily and work up to more difficult challenges. Eventually, she'll be ready for the hard stuff: frozen Kongs, which are smeared with something gooey (like peanut butter) and tossed into the freezer for a few hours.

• Treat treasure hunts. Before you leave, "hide" a few of your dog's favorite treats around the house for her to discover while you're gone. This works especially well if your dog knows the command "find it," which you can cue just as you're walking out the door.
• New toys. Always keep a stash of fun and interesting toys around, rotating in new ones from time to time. Like humans, dogs become bored with the same thing day after day. The items don't have to be new--trade toys with a neighbor or friend. The key is that they're novel to her.
• Training. Take time to teach your dog new tricks. If you aren't sure how, enroll in classes together. Even after she's mastered the basics, like "sit" and "come," regular lessons will keep her mentally sharp. Added benefit: positively-reinforced training builds her confidence and strengthens the bond between the two of you.

Physical exercise

The plusses of physical exercise are obvious (maintaining a healthy weight, for instance), but the less tangible rewards can be just as gratifying. You'll find that some of your most memorable moments with your dog happen when you're tossing her the ball at the park or hiking that trail in the mountains. Staying active together helps cement the human-canine bond.

That said, don't forget to take your well-socialized dog to the dog park or arrange for doggie play dates. Chasing and wrestling with other dogs can provide a vigorous workout, as well as fulfill her desire to hang out with members of her own species.

Agility training is another great way to stay active and bond. You don't have to take it to the competition level--many owners train simply for fun. Agility's a mental workout as well as a physical one, as your dog learns how to negotiate the various tunnels, seesaws, and hurdles of an intricate obstacle course. Plus, it's a thrill to watch your dog literally jump through hoops for you.

Bottom line: Your dog is a thinking, breathing being--and deserves to be treated as one. Keep her mentally challenged and physically active, and she'll likely stay happy and healthy. Not to mention, you'll stave off many unwanted behaviors.