For those who missed it, smartdogs' answer to my earlier query about splinting a dog's leg is well worth reading:
...dogs' legs are articulated differently than ours are; and because we can't rationalize with a dog about why we need to have him stay still and calm while we splint his leg - all pet first aid programs now recommend against splinting.
For an injury of this type [compound tibia fracture on rear leg] a sling is your best bet. You can make a very nice impromptu sling for a large dog out of a tote bag or "green" shopping bag. Just cut vertically along the two narrow (non-handle) sides of the bag to create a long, wide band of fabric with handles on both sides.
Slip the sling under the dog's chest or belly (depending on the leg affected) and one or two people can use the handles to support the dog's weight on the affected end.
Allowing the dog to use his other two legs to move helps alleviate his stress.
I'm not a large or strong person and I've successfully moved an injured 130 pound dog with a sling like this.