My non-genius canine easily escapes this crate

I bought the largest size available for my 70 lb mastiff/shar pei mix. It seems like an okay crate, but my dog is able to escape it from the top door within minutes. I'm going to attempt using a bike lock or something to prevent future escapes, but I have come home several times after very short outings (think running to the store half a block away, takes five minutes) to find my sweet boy waiting at the door instead of in his crate. He's not even particularly clever, which made us so surprised at his escapes. And yes, we make sure everything is properly latched before leaving.

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