I do have a lot of ferns and rocks that break up sight lines BUT the caves are a bit big... I think I was over estimating the size of what they were going to be when buying... I thought they would be around 2-3 inches when buying but their at an inch only... And I dont want to move the rocks around while they are in there... Too risky...They can, but on their terms. They're probably looking out while you look in thinking "Why can't this person get the set up right so we don't have to look at each other when we don't want to!"
There's no reason why you can't - it's just being creative and figuring out how. Are the caves too big? Can they see into them from other caves? Are the sightlines broken? Where are the rocks placed....