first of all that video is awsome best you tube tort video i have seen. very well put together and a perfect song . I truly enjoyed watching it and I will watch it agian and again..
as far as walking the line yes... they will stop if they can not see out... I have direct experience with this. when I first made my outdoor enclosure I used a metal fence.. they wore the grass down to the dirt. they would constantly try to get the grass on the other side even thoughn there was plenty inside the fence. I replaced it with a short wooden fence and they stopped imediatly it was like switch.. something in sulcatas is wired for getting to the other side. now they just wander all over the fenced in area and there is no more track around the fence.... go figure at least yoursa are getting plenty of exercise... as long as they aren't able to get their head stuck in the fence
(wich I was worried about) I don't think the exercise will hurt em... again nice video...i'm going to watch it again right now!!!