How to stop my 8 month old border collie/whippet cross Brian from jumping up?

I have always had Collies, my Mum in law has a Whippet cross..the whippet jumps a lot, she makes a half hearted effort to stop it, which fails. Jumping Dogs are a nuisance. When your Dog jumps up, instruct every single person you meet with the dog to do the same thing. Step quickly backwards, making a loud noise, like a 'hiss', or 'screech'..just the one time.. or similar odd sounding high pitched sound..and then turn their back to the dog. You must always do this, everyone must, the dog will only stop if it is consistent, if it gets a break and is allowed to jump a few times you are starting from scratch. Never shout at your Dog, it is a waste of time. Whippets are not known for intelligence, and are hard to train.