I would agree that rewarding calm and ignoring the excited behaviour is certainly a good start. The problem with trying to distract with toys is that he‘s learning that that behaviour is getting your attention and he‘s infact being rewarded with a game. Try not to interact at with him at all, I know its hard but even talking to him and asking him to calm down (or sit or whatever) is giving him the attention he‘s trying to get. As soon as he‘s quiet, then you can praise and give him a treat but try and do it as calmly as you can.
Introducing him to as many situations as possible certainly helps as long as you take it slowly and make sure he doesn‘t get over stressed, - my dog doesn‘t get to walk in towns very often and consequently got very worked up everytime we went anywhere fairly busy. I started taking him to town a couple of times a week, just for a few minutes at first and then built it up, I‘d sit with him outside the entrance to the supermarket and praise him when he sat quietly, let him sit at the crossing while the traffic goes past. It might even be worth trying to practise
before he has a long walk rather than afterwards, sometimes being over tired can increase the problem. I know a lot of training videos and books advocate letting the dogs race around and unwind before training but I‘ve actually found the opposite to work better for us, - first the training and then the walk or play is the reward..
My dog certainly calmed down somewhat with age (he‘s now 5) but cockers do naturally tend to be excitable dogs, they‘re ruled by their noses and every new situation brings new smells and new stimulations and that‘s when they start to get a bit overwhelmed.
Try and get everyone else on board too - ask friends and family to ignore him until he‘s quiet and hopefully
, it‘ll click with him that being quiet brings more rewards!
Hope that helps a bit!
Oh, and another thought - instead of distracting with games and treats, try getting him to sit or lie down or walk through your legs or around you- anything that gets him to concentrate on you or something which you‘ve asked him to do will take his mind off everything else, in other words, try and keep his mind occupied,.....