For the large animals that are used to migrating freely across the border to follow the water or other shifting resources , fences and walls are the same . It will cause their numbers to decrease . As far as stopping the intended migration of people , an unmanned barrier is no barrier at all . So , in the end , no matter what it looks like , a barrier will stop everything bigger than a rabbit from following scarce desert resources . It will have a guaranteed negative impact on the wildlife , but will have no impact on human migration . In the end we will have spent a massive amount of money to punish pigs , bears and antelope , and done nothing at all to stop people . If people can build a wall , people can see a way over it , no problem .