I once had a neighbour's boxer that used to jump our fence (which was big) and then come into our house via the doggy door out the back. First time it happened I had been on night shift and was asleep in my bedroom with my dog on the bed when I woke to hear this snuffling noise at the door. Had no idea wtf it was, my dog seemed quite unperturbed by it which surprised me as she was pretty protective, got up grabbed a cricket bat and went and opened the door to find this huge boxer there. I started patting him, recognised he was our neighbour's dog when suddenly he bolted and I realised he had seen my cat. Luckily she was quick and smart and bolted under a piece of furniture he couldn't get to.
On a side note he also destroyed my vegie garden with his jumping
and I removed all the stakes I had there as I was worried he would jump over and kill himself on one of them.