The border wall: the truth about what we're keeping out

Someone please enlighten me if I'm missing something, but I'm really not getting how the proposed Border Wall is supposed to keep illegal immigrants out. Read some of the completely off-topic comments about the wall on the Sierra Club's blog.
How many times have we seen news clips showing illegals simply climbing over such obstacles before? Now show me a news clip of an endangered ocelot climbing over the wall, and I'll think about giving you my blessing to build it. The plain truth is, the wall isn't going to keep them out. In fact, its quite likely that the added obstacle will only create MORE environmental damage as they try to find other ways around/under/over. Historically, walls have been a grand gesture with often enough little actual effect. But that's just talking about humans.
I hate to break it to all of you, but humans aren't really my issue. In fact, I don't even really LIKE us.
Unlike a lot of people who are reading the Sierra Club blog, I'm not focusing my concern on my job (and I happen to work in an industry fairly well inundated with illegals) , or our country's economy (that's a whole other issue!) but on what the Sierra Club is SUPPOSED to be about: The land and the animals. Conservation. As they say "Explore, enjoy, and PROTECT the planet."
It is true that illegal aliens crossing the desert often leave trash behind. Big problem, right? So lets build a big stupid ugly wall around our entire country to keep them out, that'll solve it! Not. If you Arizonans are so concerned about this trash HERE is an idea for you: Why don't you and your local Sierra Club Chapter organize a clean up day? Now I'm not saying that solves the problem, but it certainly does help, instead of sitting there at your computer bitching about garbage and the economy. When is the last time you picked up an empty soda can you found on the side of the road, honestly?