When I read the title of your post my immediate thought was - is there any other type of cocker??!!!
Have you ever allowed Oscar onto the sofa? Have any children in the house allowed Oscar on the sofa without you knowing?
Have you got a clear command -ie OFF! which you say each and every time you want him to get down? I don't say DOWN to Morgan or Cooper when I want them off the sofa, as DOWN to them means 'lie down'
This is the example that I was given by a breeder when I was phoning looking for my first pup. While explaining to me just how strong-willed cockers are, she used climbing on furniture as an example. If your cocker isn't going to be allowed on the sofa all the time, then never let him up at all. If he is allowed up, he will claim it as his own and he will not take too kindly to being told he can't climb up i,e when visitors are round. Make your rules and stick to them. She said it was confusing for the dog if the rules constantly changed - kind of made sense to me
In saying that, some people may have had success in training their cocker to jump up only when invited - I wish!!
as do my visitors (mind you everyone knows that you don't come to my house if you've got a problem with having two cockers sitting on your lap!!!)
In my sittingroom I have a navy sofa and a pale blue one - they both know they aren't allowed on the pale blue one at all (they both tried it at one stage or another - in fact Cooper really pushed it for a while there) but can climb on the other one whenever they like. Persistence and consistency is the key. It does get boring saying the same thing over again but after a while it should sink in.
Hope some of that made sense
P.S. Forgot to say Welcome to COL!!