I have been wanting to teach my dog how to be able to crawl under things and fetch them so that I don't have to crawl for her. These tips are the best way to do it.
Grab some treats and your dog and find an area with minimal distractions to begin training.
Tell your dog "down" and reward him if he complies.
Kneel by your dog and show your pup a treat.
Slowly drag the treat along the ground, just in front of your dog's nose, and give her the treat when she scoots forward on her belly to reach her reward.
Keep treats close at hand and remain kneeling by your dog.
Help your dog creep forward, inch by inch, by luring with a treat. Reward her frequently for success. If your pup stands up to get the treat, simply ask her to "down" again and reward her for lying down.
Place the treats on a nearby table and simply use your finger to guide your dog along the ground.
When your dog has crept forward a few inches, grab the treat off the table and reward her for her hard work. Continue practicing without a treat in your hand until your dog will crawl several feet at a time.
Introduce a verbal cue. After you point to the ground, tell your dog to "crawl" or "commando" or whatever command you choose. Guide your dog along the ground, following your finger..
Continue practicing crawling until your dog will crawl several feet at a time with a hand signal or verbal cue.
My dog took to these really well, it took about 3 weeks and she is now a crawling champ!