Why does my dog pee on my bed while i'm at work during the day?

Hey everyone,

I'm hoping someone might be able to help shed some light on my issue. I'm not sure there is much more I can do at this point. I have a 5 month old Maltese puppy named Buddy that I got about 2 months ago. He is a very intelligent little guy with a bit of separation anxiety which is normal for puppies his age.

He is potty trained and lets me know when he needs to go outside so this hasn't been an issue in the past. He sleeps in his crate at night without issue and gets plenty of exercise during the day. I work Monday-Friday from 9:00-6:30ish at the office but typically work from home at least 1 day a week. Very early on, I realized I did not want him to be home alone for so many hours during the day. I'm an adult and don't like being home alone that much so I figured a 5 month old puppy would have an even harder time with it.

We wake up around 7:00 AM each day - immediately go outside, go for a long walk or jog (whichever he prefers as i let him set the pace), go potty, some playtime and then I get ready for work. He turned on the puppy charm with the neighbor lady within a couple of days of getting him so I pay her to walk him twice a day and she brings him over to her place on occasion to have some company. I also have a house cleaner that comes over once a week so there are some days when he has numerous visitors giving him plenty of attention.

When I get home we typically go for another long walk or jog, play for a bit and then relax together. I make it a point to keep the same routine and come home everyday after work to see him. Same story on the weekends, aside from the occasional hour or so left home alone, I try to make it a point to do things or go places where he can come along.

While i'm at work (when he is not at the neighbors) he typically stays in my room which is connected to my bathroom, both of which have been almost entirely puppy proofed. No accessible electrical cables, TV always left on and the window sill left open so he can lay by the window and look out at the park behind the condo. He has a TON of toys to play with as I didn't want any of my furniture looking more attractive then a nice Nylabone or squeeky toy. After a couple of weeks getting familiar with his surroundings, he wouldn't even cry anymore when I was leaving for work in the morning. I would toss him his peanut butter filled kong toy, walk out the door and the neighbor said she didn't hear a peep out of him. The last couple of days has been business as usual but with the added bonus of a giant pee spot dead center in the middle of my bed. The obvious solution would be to block his access to my bed but the whole process of putting up and taking down that stuff each day starts to get annoying every day. Any idea what might be causing this? He shouldn't be marking his territory at 5 months so I was hoping you guys might be able to help. Haha sorry for the long read as well but I wanted constructive responses as opposed to people telling me i'm doing something wrong. Let me know and thanks again!