If you see a couple big sand clouds when at the edge of the dunes... Just accept your fate. I wandering into the dunes riding my raptor and had my high level direwolf with me (Had all my stuff in it) goofing around with the oasisisaur and I saw the clouds coming at me... My direwolf put up a good fight but died and I couldn't get his stuff back since they were guarding it. Just think of outer dunes as off limits for terrestrials.