I'd take Sissoos over Mesquite. Sissoos grow extremely fast if you are looking for fast growing trees. I also like Chinese Elm. Not necessarily fast growing, but I like the look. I have all 3 growing and a few others. I have vines growing along my fence - I don't know what the name of it is, but it branches out all over the place and has hundreds of yellow flowers! I also have very leafy, ground covering plant in front of my house that puts out both white and yellow flowers - lot of them! Likes water, though, especially during the summer. I can get the name of it from Whitfill's are interested, though the vines I have no clue, got them at a nursery that was going out of business. I am also experimenting with growing a Queensland Bottle Tree (not to be confused with other Australian type of bottle trees). I was at a house that was in a pond club that was doing a tour of homes with Koi ponds. One of them had a couple of these trees that had grown to 20 plus feet. Absolutely gorgeous and extremely different than most anything else you find around here and it loves Phoenix weather. If interested, there is a seller on Ebay that I bought mine from. They aren't exactly fast growing, but it's a project tree. I'm not a fan of palm trees, just my preference. They grow "wild" on my property and I have to pull them out all over the place. There is another type of desert tree growing on my property that I didn't plant but let grow. I have no idea what the names of those are, either. One of them is 3 years old and about 21 feet tall. Beautiful tree and actually gives some good shade. I saw one at a museum that they had planted a few years back, but I can't remember the name of it. I would also suggest thinking about pine trees. They are ever-so-slow growing but they can take whatever weather this city can give it, unlike my Ficus trees which sustained major damage in the recent extreme frost session we went through. I was lazy though, I could have saved them - wrap C-9 Christmas lights throughout them, especially on the tops if you can get to them and the heat coupled with covering them up does a nice job of helping them weather extreme cold. Yes, I have in the past wrapped C-9 version of Christmas lights around certain plants and trees that are susceptible to extreme cold when the forecast is for hard freeze and yes, it works. May I also suggest a Koi pond? Just for fun. Try starting with a small, preformed shell and see if you like it. Get some Koi and goldfish. They're fun to have! Small ponds don't take a lot of work and the fish learn to know you and the Koi will even come up to you! They survive the heat and the cold. I have one I made out of horse trough and 2 more that are preformed. I haven't delved into the larger type with liners - just haven't got there yet. Whatever you end up doing, have fun with it!

On the poison ivy, it's very easy to identify in the growing stage. You can see pictures on Google. All parts of the plant is poisonous as all times, so once you learn to identify the leaves, study the aerial roots and stems and avoid the plant during winter as well. It's very easy to get rid of. Cut any climbing vines and spray the rest with roundup. It will come back so let it get 2-3' ht and spray it again. Repeat this process until it is gone. If one comes in contact with it accidentally, a soapy shower will wash off the toxin. Be careful not to touch the dirty clothes again. I've been exposed and gone 20 or 25 minutes (I think) before washing it off and escaped injury. (It was awhile back so the sooner, the better.)

I am located in Northern Virginia, which I believe is zone 7. Here is a view from the "walking trail" looking up at my backyard. This is from the perspective on the other side of the black fence. and another pic. I obviously cant remove the black fence and the retaining wall with the huge 6 foot drop for safety reasons, but id like to atleast partially hide it when standing in my backyard with small trees/schrubs/bushes etc. If i can hide the black fence from view when standing up in my backyard, and hide the 2nd retaining wall, while not obstructing the view of the walking trail, that would be a win.

In terms of what plants to put there, try searching for rain garden plant lists for your area. A rain garden is usually a depression in the ground which is meant to fill with water during a storm and slowly drain, so rain garden plants generally need to be able to tolerate dry periods and wet periods, which I think would be similar to the conditions by your wall. Here's a general guide from Texas A&M: https://rainwaterharvesting.tamu.edu/files/2011/05/Rain-Garden-Plant-List-11-02-09.pdf