Around the house, I have some coral and lava rocks I have drilled and bored out to serve as natural planters. The idea is (was) to stunt or limit the growth of the plant and in some cases, the plant has escaped the confines.
The umbrella plants (trees) are an ideal plant for manipulation and getting creative with. They have interesting root structures and can adapt to changes in their environment. I gave one a titanium implant a number of months ago and it has adapted well to it: