House Trained Puppy Peeing Inside?

I have a 9 month old Bearded Collie pup. We have been very lucky in that he has hardly ever messed in the house and if he did it was on puppy pads. However over the last four days he has started to pee on the living room rug at night when we are in bed. Last night I put a pad back down at the back door where it always went yet he still peed on the carpet.

There are a couple of things that I think could be driving this. The first is that I had not been at work for the first 7 months that I have had him. Last week I went back to work and I am away from him for 12 hours a day, although my husband is still at home with him. I am concerned it might be a reaction to me not being there. However this didn't start until I had been back at work for four days. The other thought going through my head is that he had his first coat cut last week. It is very short. Anyway, as a treat we gave him a natural raw hide type chew that he has never had before. To be honest it was fairly large and probably to big for him. He ate it in one go. Since then he has been drinking more. And it was that night that the peeing started. So I am not sure whether it is connected to that. He has access to be garden all day. He goes on walks twice a day. And he always has a pee before we go to bed. Nothing has changed in his routine in that respect. Any thoughts would be appreciated and also ideas on how I can get him out of it. Thanks.