How do i keep my 2 year old in his bed?

I have a 2 and a half year old. He is still in his crib because he CONSTANTLY gets out of it. He's even opened the back door a few times. I can put him to bed anywhere from once to 15 times in a single night. Sometimes, he is up before I can even get downstairs. I've tried giving him a "calm down toy" such as a book or a glow in the dark etch-a-sketch. Some days it works.... others, not so much. I've tried taking toys, blankets, and even spankings. I'm worried about putting him in a toddler bed.... WHAT CAN I DO?!?!