My dog (Australian Cattle dog x Border collie) was trained not to pee in the house and was fine up until recently. He pees on the curtains and on chairs but we never see him doing it.  He has not done it so much sinec our other dog (anohter male) who was really dominant over him died a few weeks ago.  I was reading 'the dog listener' and it seems that it is because he sees himself as pack leader so wants to mark his territory - although this si strange as he's a very submissive dog normally. if he meets new dogs he's usually the submissive one.

Anyone know why he might be peeing and also how i could correct this?

If this is a sudden change have you taken him to the vets for a medical to rule out infection or any other causes? If its not physical might it be him marking territory now the senior dog has gone? The best thing might be to keep him busy at home to distract him, wash the areas with biological washing powder to rid the smell and be careful not to show any disgust/displeasure while you do it. He knows you dont like it as you never catch him doing it, so any attention paid to it will make it worse. HTH.

How old is he ?
Gus went through a stage at about ten months -ish where he would pee on clothing left on radiators or chairs even though he wouldnt do anything in the house normally ?
Wondering whether its just an "age" thing ??
By the way , it did pass :)