I have tried the zai and demilune techniques.They definitely help and work.Also try the one rock wall technique to slow down the water.swales and berms help too on contour.(using the a frame level)You may need to water in extreme drought.Look at the leaves of your trees they will give you a good indication if they our extremely thirsty.After the first year of planting the roots will establish themselves and you should be good.Look up Sepp Holzer if you haven't already.Hugelkulturs are also a great way to store water.Mulch Mulch Mulch definitely helps.You may need to put in some work the first year or two but after you establish your trees they should be self sustaining.Good luck on your planting.