I have been using the standard build tool, turning little boxes into big walls. I do not know how to get the walls to except the "physical" setting in the edit box without them bumping and rolling about our island, (don't even know if that would make a difference), so the pens have the default - no box checked. The animals are "physical". Have tested fences of all heights, depths, and widths; textures that are full coverage, partial coverage and transparent. Avatars cannot breach fence line. The creator is MIA, and, the best for last: the animals only escape when I"m offline. I find them in my lost and found or or under rocks or staring at the rest of the animal group fron the outside in. Help......