Rachael1983 - Yes, I think something outside may have spooked him too.
LunarBerry - I did wonder if that's what it could be. I just presumed it was maybe because I was a Girl. My Partner stays in my Flat 4 times a Week, and the other 3 days, he is a tad naughtier, but more just barky than anything else. Ye, I never really thought about the pack mentality, but that makes a lot of sense.
Maximo - He gets a lot of exercise, and I spend my Life on the floor playing. We do the tricks and treats everyday with him. But I'll see if tiring him out even more, changes anything. If not, does anyone have any advice on how I stop him barking?
Love Alexa and Oscar