I can state some real basics:-
1. Stay as low as possible at ALL times, even in areas where you think you have no chance of being seen. (I think there is maybe one place where I got up on my haunches to get past some guardtower searchlight.
2. On breaching any hilltops, there is always somewhere you can do this WITHOUT silhouetting yourself on the skyline.
3. When on the bottom of the hillside, always crawl along the side where the guard is; because they obviously have problems peering off the edge. Unless the area on the opposite side is darker or in shadow.
4. Be aware of the surface type you are crawling on and use the quieter ones, and avoid trying to crawl through any vegetation, even if it DOES appear to be giving you cover.
5. If a guard should cry out for ANY reason - STOP! And don't make any moves until he calls an all clear to his comrades. And further, if he should cry out a second time very quickly after you have begun to move again, I would strongly advise seeking out an alternative route without any further probing from that direction.
6. You will perhaps find yourself approaching the same spot with the perception it is the ONLY route through, and in at least one instance you will be right. However, you may have to go several times before you win through on that particular point.
7. Perseverence and patience will always remain the biggest factors to success - if you like sniping, this is something which will come natuarally to you.
Again, if you are still finding it impossible, I would also be prepared to go through as much of it with you as I can. Didn't we have a write-up on one of the forums at some stage?