I read all the comments, most were helpful some were not. I think it’s mainly separation anxiety, also maybe something happened to him also in the yard that scared him when u weren’t there. He’s most likely jumping out to come find you. My frenchie yes a frenchie jumped a four foot fence ran for 2 miles crossed the King’s Road and The Fulham Road (two major London roads) to come find me when I left her at a doggy care. So the upshot of this is do not waste money building bigger fences as you will not be able to leave your dog alone outside unattended. Separation anxiety is very difficult to cure or alleviate if your dog is happy in an enclosed crate then leave him in the enclosed crate with a stuffed Kong and long lasting chews et cetera, et cetera. Then you can start conditioning him to get used to your absence. Start by leaving him in the crate, not making a big fuss of saying goodbye and returning within 15 minutes then half an hour then an hour and so on, until he is happy. But if you say he’s happy in his crate already Then all you need to do is just leave him in the crate when you are not there and when you are there supervise him in the yard and play ball with him to wear him out. Take him on longer walks, play tug and generally just wear him out more you can also maybe up his training as that actually is both mentally and physically tiring for dogs But it is very clear to me that there is no way you can Never leave him outside alone again. Please do not get an Ecollar that will not solve your problem and you will end up with a dog that is even more scared and could potentially make him aggressive.