Hi, my 9 month old cavalier has started to piddle up against things in the house.  He is normally extremely clean.  If I get him castrated, will this put an end to this problem??

It might help, but if he's marking - are you cleaning away the scent efficiently enough?  To acheive this, the best way is to use a warm solution of biological washing powder, and then spray the surface with white wine vinegar or white spirit - the breaks down the fatty acids that hold the scent and encourage him to wee again.........

Not necessarily.  Do you have bitches around as well or bitches in season?  Can he get outside to urinate if he wishes to?  Is it sudden and frequent - could he have a urinary infection (or it might just be he is getting a testosterone surge)