I'd think about a Corgi. I'm thinking it would be like an Aussie, but couldn't jump our four foot fence.
We had a corgi. He was a shelter special and he was about 7 when we adopted him, but apparently he had some hearing ear dog in his past as he’d signal us when the phone rang or the doorbell rang and exhibited other similar training. He was very well trained and quite disciplined. He insisted on going to bed every night at 8, trotting down the hall to his bed. We called him our little military dog. He lived to 20. I still miss him.