Soooo I have a 12 week old border collie (Coda) who is still 1 week away from his second jab and cant go out properly! so has so much pent up energy all he does is terrorise my yorkie (Alfie).. they cant be out with one another as Coda constantly chases him and "plays" with him but Alfie just wants to lay around and so gets aggressive towards him.

How can I try and prevent this? I know the answer is to exercise both dogs and then let them chill together but Coda is the main culprit and he is unable to go out properly yet. How can I ware Coda out enough to try and let them hang out?

Exercise alone will never tire a collie out they need to use their brains. At this age before walks can begin (And then it will only be short walks for months yet ) you need to be training in short bursts, lots of mental exercise is needed and to be honest you need to be able to shut the puppy away from your Yorkie until he is a little better with his manners. It's unfair to have him constantly pestering.
I would do 5 minutes of brain work every hour or so and the rest of his waking time you can use to train him informally by asking for sits, downs, turns etc.. as you move around the house together. Make sure you have some playtimes as well it's up to you to play with him and not up to your other dog. At this age distraction is the best way to stop him so if he is winding up the Yorkie then distract him into a better game. If he won't stop and the Yorkie is getting fed up then a puppy pen and some chews or toys till he has settled down again is your best option.
Aileen

`That's Brilliant, will start doing a lot more brain games!! he is picking up the sit, down etc so well but just has so much energy!

Will give your advice a go for sure thank you.

Have a look at the Kikopup videos on her website. She is a very good trainer and there a lots of trainng games demonstrated

I agree, lots of games and brain training, the leave command might be top of your list, would your little dog be happy if he was caged for a while to give him an rest from the puppy or maybe he would be glad to be chilling on your bed alone