What can I do to break my dog of her horrible habits of not wanting to go outside?

I have an 8 year old bet and coon hound mix who has recently decided she doesn't want to go outside and would rather go in the house when everyone is asleep. She was biting anyone who tried to put a leash on her but i solved the problem by leaving the leash on at all times. I took her to the vet who said she was fine and it was a training problem. I agree but I don't want to use a shock collar like he said. What else can I do? I've looked at the citronella spray collars but they're still a little too expensive.