Easy, and neatest way to geo-merge on Sandbox?

I've been searching for a while now and I can't find a straight answer. I've tried using the tear-drop method, but I can't get the tear low to the ground. I'm asking because I'm currently working on a sandcastle (for the Forge Cafe contest) and i'm building a huge wall......thats supposed to go into the dunes. So what I'm asking is, can somebody give me a detailed guide to actually geo-merging into the dunes.

Any help would be greatly appreciated, thanks.