We crate trained our lab for over a year from when she was about 5 months old. We had the luxury of my husband being able to go home at lunch to let her out on the days I was away for more than 6 hours (I was in grad school with a very flexible schedule and lots of working from home).

Before we started the crate training she chewed up hundreds of dollars in books and shoes.

She balked at the crate at first but definitely came to see it as her space. We started by feeding her in it, so she would associate the crate with a good thing, FOOD. Then she'd go in there for naps on her comfy blanket on her own while we were home. Soon it was no problem for her to run in there when we left the house. She began to associate keys with her crate so that if one of us picked up our keys, she'd run right into her crate, happy as a clam. All of this while our other, older, perfectly behaved dog got to wander the house and yard freely. The lab didn't seem to mind, she loved her crate.