I would think that 2" would be enough to prevent them from
accidentally falling off the upper level. However, intentional departures are another question. I have two lofts in my cages with about 2" rails and the pigs just jump over the edge. That's not a problem in my cage because it's a one level cage so the loft is maybe 6-8" above the floor. Is an entire grid height too much for jumping?
Speaking of cages, I uploaded my pictures to the gallery. I hope this link is correct:
http://www.cavycages.com/photos/show...500&ppuser=336