Decided to try an old trick.
Took Luke and my other dog to the hills.On the way I stoppep to let my Pyr run behind my truck for excercise and so Luke wouldn't think I was abandoning him when I did my first lesson with him. (Extremely rural forest service land, no traffic hardly at all and very rough roads so no one can travel fast.)
When Lukes turn came I let him out and stood until he was 50yrds away and no longer looking back to check on my whereabouts, stepped in truck and drove 1/4 mile before I saw him come back onto the road. I stopped to let him catch up and put him back in the truck, (I wouldn't have done this if the Siberian was more dominant than the German Shepherd).
Proceeded to some hilly terrain with slopes ranging 45 to 70 degrees to let them excercise and try an idea. Take care of the rambling spirit, and teach him awareness of his proximity to me.
To prepare I had placed a harness (for safety) and attached a light springy 25' long line on him.
When we arrived I let my Pyr run wild for distraction and Luke drag the long line. Whenever Luke would try to take off after the Pyr, or I noticed he was no longer aware of me, I would pick up the long line and tug or change directions. On those slopes, with a bedding of dry slippery leaves, and pine needles (His safety foremost in my mind, I would have been able to catch him with the harness had I needed.) a light tug when I reached the end of line would cause him to loose his footing and scramble for traction.
Worked better than hoped. Spent two hours walking/crawling up slopes. By end of first hour my Pry ran by while Luke was in a creek and I was resting, Luke actually made a step to start running after him, looked at me, and ran to me instead.
During the next hour he started glancing back more to check on my whereabouts. Everytime he did so I marked it with praise, or a pat if he happened to be close enough. After a while he learned he could plant his feet on the slopes and have a blast sliding down.
After returning home I left the long line on Luke and left my Pyr out for a while to see if I would get the same reactions at home. Success.
Also found I have to keep a close eye on him. He has gone to the opposite end of the spectrum regarding heights. He will now actually seek them out with much less caution than Siberians I had years ago.