I'm so sorry, I geuss it realy was time for old Duke to leave this earth.
I know you will miss him dearly but he'll always be in your heart no matter what & he gave you a gift that can never be taken away, a gift of pure joy and love rapped with a warm doggies heart and stuck together with a forever tied friendship between you and your little sweet Duke.
Bless you Duke may you be at peace forever now! :(
Here is a video of rainbow bridge for you, please take care.
http://www.indigo.org/rainbowbridge_ver2.html