I'm truly sorry that you're the ones that have been forced to make this heartbreaking decision.

Mr Biggles should never have been re-homed in the first place. It seems that there is a never ending number of pet owners that let their dogs get away with unacceptable behavior for years. Then one day they've had enough and dump the dog in a shelter.

They're just ignorant enough to think that there are hundreds of wonderful doggie retirement homes lined up just waiting to take their older problem pets off their hands. They convince themselves that the dog will be "better off" and will live "happily ever after". It seldom works out that way!