I would go back to 'puppy' training - you say he has always done it but only in the lounge. I would restrict him to the kitchen or area that is easy to keep clean. I would also invest in a crate and let him go in it to sleep, chew, etc for short periods, letting him out for a wee (stay out with him till he has done one or two). Bring him back and put him in the crate for a short while with something to chew on. Take him for longer walks so he gets lots of chances to go, and praise madly when he does using a trigger word or phrase like 'good boy do wee wees' or something you are comfortable with! When you let him out of the crate take him straight out for a wee. Basically restricting the opportunity for doing it indoors. Hopefully he will learn what is expected of him, but it might take time as you have not done anything about it so far. Do not scold him, particularly as you say he is nervous. Do not use the crate as a punishment, make it his 'den' with a blanket and lots of toys/chews. Neutering won't stop this as its 'learned' behaviour that he has been allowed to get away with so you need to go right back to the beginning and house train him like you would a baby puppy. However neutering might calm him down and make him less hormonal and wanting to mark his territory. The biggest thing will be to give him something to think about so try obedience classes because Border Collies were bred to work all day and get bored very easily.