This is really hard, especially for older dogs that have been successful at jumping up - no matter how hard you've tried!
My friend has a great dane that LOVED to jump on people ... she tried everything - dropping food on the floor, turning her back to him (he'd still jump and paws would be on the shoulder from the back - eek!)
She finally found something that worked. When someone came to the door, she would unlock the door, back up a bit, have him on leash and she had the leash on the floor and was standing on it. He was laying down. She'd then tell the people to come in - and he couldn't jump up because she was standing on the leash. (She had her legs spread about 12-18 inches apart, along the length of the leash that was on the floor), and she was hold the loop of the leash in her hand. The dog had about 4-6 inches of "loose leash". He could raise his head, etc. but he wasn't able to get up.
If you're standing "square" you'll be able to keep your balance. It took a couple of different people that she practiced with, but it didn't take him that long to figure it out. Now, he doesn't jump on people at all!
Marion’s Zoo-Kyleigh, Raylan-cat, Echo-TAG,