African Sumac Too Close to a Wall?

Q. I am considering planting three, 22" box African sumacs along a 40' block wall behind a 1.5' retaining wall. Is this feasible? How far away should they be from the block wall? Is there a better option for shade that isn't poisonous to dogs and that have no invasive root issues?

African sumac planted near a wall flowering in February

 A. 80% of all landscape plants are poisonous. If your dogs eat enough of any of your plants, they can get sick. 

Plant them no closer than 3 feet to the wall and 4 feet would be better, and 8 feet is ideal. This tree can grow to 40 feet and consumes a fair amount of water. These trees are really not intended to be used for planting along tall walls because of their shape. 

Put your permanent irrigation away from the wall so that roots will grow in that direction and less towards the wall. It is very difficult for me to make plant recommendations when I don't know what is available. Consult sites such as the plant list found at the Las Vegas Valley water District  and consult with your local nursery about availability of the plants that you like.