We've been working on this one for a little while. Teaching back up from a distance has been difficult for me and Gracie, but Rach got it right away.
First Mum started by teaching him very close, with him facing her. Then she stepped into him just a little and when he backed up she clicked, said beep, beep, and threw a treat between his legs (this is key in getting the distance she's discovered over the years).
Then when he started understanding that the 'beep, beep' and click meant to back up she started increasing the distance, always throwing a treat to him, instead of having him come back to Mum for a treat (again, this is key to get the distance).
Once he really got it down, he started doing the 'throw his head up and barking a little,' silly boy! But Mum thinks it's cute.
She then had him increase and increase the distance, and then working with him in different places, like down this hall, through the kitchen, upstairs, and outside. Now even though this video shows him backing up about 15', he can actually do about 30' feet now outside.
Check it out!