What about somewhere near your new water feature? You could water them any time you added water to it. Or try 5 by the holly and put the other 5 into a big container (with or without other plants), either with a wick and a saucer (with mosquito bits) or use a container with a self-watering reservoir base. The container would be for backup, in case the holly location doesn't work out, and would let you "hold" them while you work on the water feature and pergola.
