My ferret will not stop cage biting/scratching?

my ferret scratches and bites his cage when he wants to come out and is bored, i have tried putting apple bitter on the cage where he bites but it does not deter him and i don't want to let him out because it will encourage it. i let him out multiple times a day and even take him for a walk to the park sometimes. the cage biting has to stop though. help plz?