How can I train my dog ASAP so the pound doesn't kill him!?

Hes 3 yrs old, a beagle/terrier mix. Problem: hes been in a cage most of his life,except when he goes outside. Thats my parents doing.. And now he cant be out in the house cuz he chews everything and bothers the cats, he has to be on a chain outside cuz we dont have a fence, he barks and nips at EVERYBODY no matter how well he knows them. Im going into the hospital for a week and we have to put him in the pound until we get back, but theyll just put him down. How can i make him a nice dog in 1 month?!?