Separation anxiety? in a cockapoo

Question
I have had my dog for 10+ years, he has been in a kennel only 3 times since we have had him. When we first had him we would confine him to the bathroom in the basement so he could walk around but not walk around in the house. Last year he started scratching at the door until he wore away the door frame. Today he actually scratched until he tore into the drywall of the bathroom. What can we do?  

Answer
How often and how long is this dog confined for?  Does he have anything to play with while he is confined?  Are food and water provided for him while he is confined?  Does this dog get time to play in the backyard or get walked after being confined?  Does he get time to play with the family after being confined?