Hey dudes. I've been with my girlfriend for over a year now and we've lived together for a majority of that time. She's a huge dog lover, has owned multiple in her lifetime, and has begged me for a dog since we moved in together. I've always said no. Over the past 6 months we've been dogsitting her coworker's bulldog every few weeks for days at a time and I have warmed up to the idea of having our own, mostly because it would make her so happy, and also would give me peace of mind that she is not alone at night while I'm on the road. I want to surprise her this Christmas and get her (technically us) a dog. I know absolutely nothing about breed characteristics, so I wanted to list out our living conditions and see what breed would work best for us. 

1. We live in a 1 bedroom apartment in LA. It's pretty big, especially for LA. We will be upgrading to a 2 bedroom in 2018, but we will probably be in apartments for a good while due to insane real estate costs in LA-proper. Obviously this isn't conducive to a large dog, but I don't want a little lapdog either. I would say something larger than a Pomeranian, but smaller than a Pit Bull/Labrador

2. I travel a ton for work, and my girlfriend is home alone quite a bit. We live on a ground level apartment, so I would like a dog that would be aggressive enough to at least raise hell if an intruder were to try and enter, but I don't need an attack dog or anything. 

3. My girlfriend is a big time fitness hiker. She does Runyon Canyon a few times per week. When we are dogsitting the bulldog, because of the respiratory problems that are inherent to bulldogs, the dog simply cant hang on the hike. So I would like a dog that has enough stamina to make it on a solid 45 minute hike with her. This is a big reason I am asking this forum question, because I loved that bulldog, but the hikes are such a big part of my girl's life. If it weren't for the hikes I would def get a bulldog. 

4. My father in Ohio has some minor dog allergies, but he seems to do much better with short haired dogs. I would like something with short hair so he isn't uncomfortable when he visits us. 

So in short, I would like something mid-size, short haired, with good stamina for hikes/walks, and will react to strangers trying to enter our apartment. I'm not worried about the cost of the dog itself. I've obviously been spending hours researching on the internet, but first hand testimony is far more valuable to me. Please share your experiences and let me know if any of you any recommendations.