training my dog  

Rewarding him with food is training him not to walk or rather he is training you to feed him when he refuses! It is common of dogs of this age to rebel against training you must force him to walk. Ignore him and just keep walking even if you drag him along, reward him only when he co-operates. He will soon learn

all the best urban

Walking on a leash is often the hardest trainable trick to teach a dog. They either want to pull out of control or do as your dog is doing and simply lay down and not move. If you have someone you can partner with try having one person walk in front of him walking backwards (make sure you do this somewhere that there is no chance of them falling) while the other person holds the leash and actually walks him. The person that is walking backwards should be giving praise and encouragement. Also teach him a walk command. We use "Lets Go" as our command when training so that the dog knows what you are asking him to do. Also, I would strongly encourage you to enroll him in a puppy training class. He is going to be a big guy and training in is early life will make your life much easier. I know that there are several AKC recoginized classes in my area that will teach you to teach him the basics.

Best of luck with him.